Eu2+ and Eu3+ based "concentrated phosphors" as converters for UV LED light: two approaches and two new examples - Batentschuk, Miroslaw; Geisler, R.; Hum, Jasmin; Iqbal, Farasat; Meister, Frank; Osvet, Andres; Stiegelschmitt, Alfons; Winnacker, Albrecht (Applied Physics B-Lasers and Optics, 2012)
The absolute majority of phosphors are composed of a host lattice and some percentage of an activator. At higher activator concentrations the concentration quenching occurs. However, there are phosphors in which only minor quenching of the emission occurs with increasing of the activator content. Based on the existence of two different valence states of the Eu ion (2+ and 3+), two approaches for the development of "concentrated phosphors", i.e. light emitting materials in which the activator ion is a main part of the crystal lattice, are discussed. In both approaches, reduced energy migration leading to the luminescence quenching is considered as a main condition to reach a high quantum efficiency of a concentrated phosphor. Two kinds of phosphors-Eu2+-doped alumosilicate and Eu3+-doped oxyfluoride-are used as an experimental basis for this discussion. Starting from the stoichiometric Ca1-x Eu-x(2+) A1(2)si(2)O8 anorthite and Eu3+OF oxyfluorides, the non-stoichiometric powders with Eu-0.92(2+) A1(1.76)Si(2.24)O(8), Eu3+(O, F)(2,35) and Eu3+(O, F)(2,16) compositions were synthesized by a solid state reaction and investigated. It was shown that-in spite of the almost 100% Eu concentration-light converters with high quantum efficiency of more than 45% can be realized. A possible application of these materials as UV LED light converters for white light emitting diodes are discussed as well.

Evaluation of Electron Donor Materials for Solution-Processed Organic Solar Cells via a Novel Figure of Merit - Min, Jie; Luponosov, Yuriy N.; Cui, Chaohua; Kan, Bin; Chen, Haiwei; Wan, Xiangjian; Chen, Yongsheng; Ponomarenko, Sergei A.; Li, Yongfang; Brabec, Christoph (Advanced Energy Materials, 2017)
Organic photovoltaic (OPV) technology offers many advantages, although no commercial applications have been achieved after more than a decade of intensive research and development. Several challenges have yet to be overcome including high power conversion efficiency (PCE), good processability, low cost, and excellent long-term stability, and so on. In this article, these fundamental challenges are significantly addressed by surveying and analyzing a new merit factor for material applied accessibility containing three parameters: synthetic complexity, device efficiency, and photostability. Thirty-five donor small molecules are introduced to assess their synthetic accessibility. Furthermore, the PCEs and device photostability of these molecules are carried out, and further measured under one sun illumination within 200 h, respectively. Combining with the characteristics of these three factors, investigated molecules are ranked according to an industrial figure of merit (i-FOM), while some guidelines for the material design and synthesis are given. It is suggested that a PCE of >14% and an i-FOM of >20% via active material engineering are realistic for possible industry future of OPV. Along with the systematic study, it is believed that this i-FOM can be taken into consideration at an early stage of molecular design and provides valuable insight for efficient evaluation of photovoltaic materials for possible commercial applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Conversion efficiency; Efficiency; Molecules; Solar cells; Synthesis (chemical); Transportation; Figure of merits; Long term stability; Low costs; Power conversion efficiencies; Processability; Organic solar cells

Evaluation of n-type doping of 4H-SiC and n-/p-type doping of 6H-SiC using absorption measurements - Wellmann, Peter; Bushevoy, S.; Weingärtner, Roland (Materials Science and Engineering B-Advanced Functional Solid-State Materials, 2001)
A non-destructive, absorption measurement based optical method has been developed in order to determine doping type (n- or p-type), doping level and doping level distribution in 4H and 6H silicon carbide (SiC) wafers. The bandgap absorption has been calculated numerically taking into account band filling, band shrinkage and band tailing effects which al e a function of donor and acceptor concentration N-D and N-A, respectively. The numerical results Lire compared with experimental data. A calibration plot of the doping dependence of the absorption of n-type 6H SiC is presented and the application for mapping of the SiC wafer duping level distribution is demonstrated. (C) 2001 Elsevier Science B.V. All rights reserved.
Keywords: Silicon carbide; Absorption measurement; Charge carrier concentration; Mapping

Evidence of Tailoring the Interfacial Chemical Composition in Normal Structure Hybrid Organohalide Perovskites by a Self-Assembled Monolayer - Will, Johannes; Hou, Yi; Scheiner, Simon; Pinkert, Ute; Hermes, Ilka M.; Weber, Stefan A.L.; Hirsch, Andreas; Halik, Marcus; Brabec, Christoph; Unruh, Tobias (ACS Applied Materials and Interfaces, 2018)
Current-voltage hysteresis is a major issue for normal architecture organo-halide perovskite solar cells. In this manuscript we reveal a several Å thick Methylammonium Iodide (MAI) rich interface between the perovskite and the metal oxide. Surface functionalization via selfassembled monolayers (SAMs) allowed us to control the composition of the interface monolayer from Pb poor to Pb rich, which in parallel suppresses hysteresis in perovskite solar cells. The bulk of the perovskite films is not affected by the interface engineering and remains highly crystalline in surface normal direction over the whole film thickness. The subnm structural modifications of the buried interface were revealed by x-ray reflectivity (XRR), which is most sensitive to monitor changes in the mass density of only several Å thin interfacial layers as a function of substrate functionalization. From Kelvin probe force microscopy (KPFM) on a solar cell cross section study, we further demonstrate local variations of the potential on different electron transporting layers (ETLs) within a solar cell. Based on these findings we present a unifying model explaining hysteresis in perovskite solar cells, giving for the first time insight into one crucial aspect of hysteresis and paving the way for new strategies in the fields of perovskite based opto-electronic devices.
Keywords: perovskite solar cell; hysteresis; buried interface; x-ray reflectivity; Kelvin probe force microscopy

Evidencing Excellent Thermal- and Photostability for Single-Component Organic Solar Cells with Inherently Built-In Microstructure - He, Yakun; Heumüller, Thomas; Lai, Wenbin; Feng, Guitao; Classen, Andrej; Du, Xiaoyan; Liu, Chao; Li, Weiwei; Li, Ning; Brabec, Christoph (Advanced Energy Materials, 2019)
Solution-processed organic solar cells (OSCs) are promising low-cost, flexible, portable renewable sources for future energy supply. The state-of-the-art OSCs are typically fabricated from a bulk-heterojunction (BHJ) active layer containing well-mixed donor and acceptor molecules in the nanometer regime. However, BHJ solar cells suffer from stability problems caused by the severe morphological changes upon thermal or illumination stress. In comparison, single-component organic solar cells (SCOSCs) based on a double-cable conjugated polymer with a covalently stabilized microstructure is suggested to be a key strategy for superior long-term stability. Here, the thermal- and photostability of SCOSCs based on a model double-cable polymer is systematically investigated. It is encouraging to find that under 90 °C & 1 sun illumination, the performance of SCOSCs remains substantially stable. Transport measurements show that charge generation and recombination (lifetime and recombination order) hardly change during the aging process. Particularly, the SCOSCs exhibit ultrahigh long-term thermal stability with 100% PCE remaining after heating at temperature up to 160 °C for over 400 h, indicating an excellent candidate for extremely rugged applicatio
Keywords: device stability; double-cable conjugated polymers; thermal- and photostability; organic photovoltaics; single-component organic solar cells

Evolution and stability of basal plane dislocations during bulk growth of highly n-type doped versus highly p-type doped 6H-SiC - Sakwe, Aloysius; Müller, Ralf; Queren, Desiree; Künecke, Ulrike; Wellmann, Peter (Physica Status Solidi (C) Current Topics in Solid State Physics, 2006)
The movement of basal plane dislocations (BPDs) in SiC enhances the formation of stacking faults (SFs), which are believed to be a major hindrance in realizing SiC based bipolar devices of high performance and reliability for high power device applications. In this work, we report for the first time on the evolution and stability of BPDs in highly p-type doped SiC compared with conventional highly n-type doped SiC for improved bipolar devices. Using sequentially doped p-type / n-type / p-type SiC single crystals (sequential doping was done in single growth runs) we investigated the occurrence of BPDs in n-type doped SiC versus p-type doped SiC to address their evolution and stability depending on doping type. We have found, that BPDs are absent or appear significantly less pronounced in p-type doped SiC as compared to n-type doped SiC, a phenomenon which is of great importance to the stacking fault problem in SiC and hence to the performance and reliability of SiC based bipolar devices. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: SiC; basal plane dislocations; stacking faults; bipolar devices; n-type doping; p-type doping

Evolution of cell cracks in PV-modules under field and laboratory conditions - Buerhop, Claudia; Wirsching, Sven; Bemm, Andreas; Pickel, Tobias; Hohmann, Philipp; Nieß, Monika; Vodermayer, Christian; Huber, Alexander; Glück, Bernhard; Mergheim, Julia; Camus, Christian; Hauch, Jens; et al. (Progress in Photovoltaics, 2017)
Damaged modules, especially with cell cracks, can be observed quite often in photovoltaicinstallations. Little knowledge exists about long‐term stability of precracked modules at real operating conditions. Previous investigations and existing standards focus on the degradation of new, defect‐free modules. This work highlights a twofold approach for life‐time study of precracked modules: (1) outdoor exposure of 54 precracked modules for 1 year and (2) artificial stressing of 20 representative precracked modules with a novel load test setup simulating snow and wind loads. The outdoor exposure reveals that at moderate weather conditions, no changes were detectable, neither in electric performance nor in EL‐images. However, the accelerated static load tests with stepwise increasing pressures point out that above a certain threshold, cracks grow. Below this threshold, formerly unseen cracks become visible at the loaded stage. In addition, modules with a smaller number of damaged cells have a stronger tendency to degrade further than modules with an already large number of cracked cells. Remarkably, the power output measured with a solar simulator after a stress test up to 2500 Pa (describing conservative proof conditions for severe snow loads according IEC 61215) remains unchanged for almost all modules.
Keywords: cracks; electroluminescence; field test; mechanically loading; performance; pre‐cracked modules

Evolution of inverter ground impedances for PV modules with various backsheet types - Buerhop, Claudia; Stroyuk, Oleksandr; Pickel, Tobias; Hauch, Jens; Peters, Ian Marius (Progress in Photovoltaics, 2022)
Herein, we present results that emphasize the importance of retaining high insulation resistance in polymer backsheets for the reliable operation of photovoltaic installations. By correlating inverter monitoring data, meteorological data, and spectroscopic information from backsheet materials of photovoltaic modules, we derive performance and degradation rates for inverters connected to photovoltaic modules with several backsheet types. The feasibility of evaluating the degradation status of photovoltaic modules in the field through spectroscopic analysis of the water content in backsheet and encapsulant is demonstrated. We show that an increase in water content is a sign for reduced leakage resistance. Ground impedance was measured alongside relative humidity and temperature for three specific backsheet types. Inverters with polyamide and fluorinated coating/polyethylene terephthalate backsheets showed a significant drop in ground impedance at high humidity, RH > 70%. A loss rate of −2 kΩ/day in ground impedance was found for inverters connected to modules with certain fluorinated backsheets. This value is twice as high as for inverters connected to modules with polyamide backsheets. Time series show that the sensitivity to moisture and water ingress increases with time, especially for modules with polyamide and certain fluorinated backsheets. The worst degradation scenario observed had an annual yield loss of 27% due to inverter outages on humid days. About 25% of inverter trip alerts after 8 years of operation included modules with the specific fluorinated backsheet. In general, the study revealed a distinct backsheet impact on ground impedance and operation of inverters and the resulting yield showing an important role of the choice of polymers for reliable and long-lasting photovoltaic systems.
CRIS-Team Scopus Importer:2022-09-16
Keywords: degradation; ground impedance; insulation resistance; near-infrared spectroscopy

Excited-State Interaction of Semiconducting Single-Walled Carbon Nanotubes with Their Wrapping Polymers - Kahmann, Simon; Salazar Rios, Jorge M.; Zink, Matthias; Allard, Sybille; Scherf, Ullrich; Dos Santos, Maria C.; Brabec, Christoph; Loi, Maria A. (Journal of Physical Chemistry Letters, 2017)
ABSTRACT: We employ photoluminescence and pump−probe spectroscopy on films of semiconducting single-walled carbon nanotubes (CNTs) of different chirality wrapped with either a wide band gap polyfluorene derivative (PF12) or a polythiophene with narrower gap (P3DDT) to elucidate the excited states’ interplay between the two materials. Excitation above the polymer band gap gives way to an ultrafast electron transfer from both polymers toward the CNTs. By monitoring the hole polaron on the polymer via its mid infrared signature, we show that also illumination below the polymer band gap leads to the formation of this fingerprint and infer that holes are also transferred toward the polymer. As this contradicts the standard way of discussing the involved energy levels, we propose that polymer-wrapped CNTs should be considered as a single hybrid system, exhibiting states shared between the two components. This proposition is validated through quantum chemical calculations that show hybridization of the first excited states, especially for the thiophene−CNT sampl

Exfoliated CrPS4 with Promising Photoconductivity - Budniak, Adam K.; Killilea, Niall Andrew; Zelewski, Szymon J.; Sytnyk, Mykhailo; Kauffmann, Yaron; Amouyal, Yaron; Kudrawiec, Robert; Heiß, Wolfgang; Lifshitz, Efrat (Small, 2019)
Layered semiconductors have attracted significant attention due to their diverse physical properties controlled by composition and the number of stacked layers. Herein, large crystals of the ternary layered semiconductor chromium thiophosphate (CrPS4) are prepared by a vapor transport synthesis. Optical properties are determined using photoconduction, absorption, photoreflectance, and photoacoustic spectroscopy exposing the semiconducting properties of the material. A simple, one-step protocol for mechanical exfoliation onto a transmission electron microscope grid is developed, and multiple layers are characterized by advanced electron microscopy methods, including atomic resolution elemental mapping confirming the structure by directly showing the positions of the columns of different elements' atoms. CrPS4 is also liquid exfoliated, and in combination with colloidal graphene, an ink-jet-printed photodetector is created. This all-printed graphene/CrPS4/graphene heterostructure detector demonstrates a specific detectivity of 8.3 x 10(8) (D*). This study shows a potential application of both bulk crystal and individual flakes of CrPS4 as active components in light detection, when introduced as ink-printable moieties with a large benefit for manufacturing.
CRIS-Team WoS Importer:2019-12-13

Experimental efficiency of a low concentrating CPC PVT flat plate collector - Pröll, Markus; Osgyan, P.; Karrer, H.; Brabec, Christoph (Solar Energy, 2017)
PVT collectors aim to solar co-generation of electricity and heat. An new concept raises thermal efficiency by concentrating sunlight with CPC reflectors, in order to access a higher number of solar thermal applications. Losses in PV efficiency due to a higher operating temperature are accepted with regard to a higher overall collector efficiency. As a side effect, the concentration lowers the material usage of PV and enables a high efficient thermal coupling of the PV cell to the heat carrying fluid. The work focuses on the construction, as well as on the angle dependent electrical and thermal measurement of the real-size CPC PVT collector prototype (1460mm×600mm×150mm). In previous publications, calculations and experiments studied the influence of the CPC reflectors on the PV efficiency. Further, the thermal coupling between PV cell and heat carrier fluid has been measured in a lab experiment. These results, together with transient annual simulations, were considered in the design process of the CPC PVT prototype with an angular acceptance range of ±25°. The experiments were conducted on the outdoor solar test facility at ZAE Bayern in Garching, Germany. The thermal and PV efficiency has been measured with MPP tracking, as well as for open circuit voltage for fluid temperatures up to 107°C. It could be shown, that the thermal efficiency while MPP tracking is elevated to 34% compared to a glazed flat plate PVT with 17% for collector temperatures 60K over ambiance. At the same time, the electrical efficiency drops from 15% cell efficiency to an overall collector efficiency of 9%, due to the optical setup, temperature effects and a non-uniform flux distribution caused by the reflectors.
Keywords: Collector; Concentration; CPC; Experimental; Flat plate; Fluid; Hybrid; PV; PVT; Solar; Solar thermal

Exploring the Effect of Polymer Addition to the Room Temperature Synthesis of Colloidal Lead Halide Perovskite for Better Stability, Higher Passivation, and More Uniform Particle Size - Darwish, Elshaimaa; Elia, Jack; Batentschuk, Miroslaw; Osvet, Andres; Brabec, Christoph (Advanced Engineering Materials, 2025)
In recent years, metal halide perovskites have emerged as a promising alternative to existing semiconductor materials in many applications due to its appealing properties. Despite perovskite huge potentials in many applications, they are still suffering from different kinds of stability issues that are hindering their marketability. Several attempts to stabilize perovskites including polymer encapsulations and inclusions of perovskite materials into polymer matrices due to the stability against moisture that the polymer can offer. Nevertheless, the polymer is acting as an unreactive component without any role into enhancing the optical properties of the studies metal halide perovskite. This study examines the incorporation of the polymer BUTVAR (polyvinyl butyral [PVB]) in the production of various perovskite structures at room temperature: CsPbBr3, Cs2PbBr5, FAPbBr3, and MAPbBr3. The study demonstrates that the incorporation of the polymer solution enhances the optical characteristics and improves the shape uniformity of the resultant perovskite material without altering the inherent structure of the original perovskite material. Furthermore, it improves the durability of the acquired particles against UV irradiation.
CRIS-Team Scopus Importer:2025-04-11
Keywords: perovskite nanocrystals; perovskite nanoparticles higher passivation; perovskite stability; polymer addition to perovskite nanocrystal synthesis; room temperature synthesis

Exploring the Limiting Open-Circuit Voltage and the Voltage Loss Mechanism in Planar CH3NH3PbBr3 Perovskite Solar Cells - Chen, Shi; Hou, Yi; Chen, Haiwei; Richter, Moses; Guo, Fei; Kahmann, Simon; Tang, Xiaofeng; Stubhan, Tobias; Zhang, Hong; Li, Ning; Gasparini, Nicola; Ramírez Quiroz, César Omar; et al. (Advanced Energy Materials, 2016)
Perovskite solar cells based on CHNHPbBr with a band gap of 2.3 eV are attracting intense research interests due to their high open-circuit voltage (V) potential, which is specifically relevant for the use in tandem configuration or spectral splitting. Many efforts have been performed to optimize the V of CHNHPbBr solar cells; however, the limiting V (namely, radiative V:V) and the corresponding ΔV (the difference between V and V) mechanism are still unknown. Here, the average V of 1.50 V with the maximum value of 1.53 V at room temperature is achieved for a CHNHPbBr solar cell. External quantum efficiency measurements with electroluminescence spectroscopy determine the V of CHNHPbBr cells with 1.95 V and a ΔV of 0.45 V at 295 K. When the temperature declines from 295 to 200 K, the obtained V remains comparably stable in the vicinity of 1.5 V while the corresponding ΔV values show a more significant increase. Our findings suggest that the V of CHNHPbBr cells is primarily limited by the interface losses induced by the charge extraction layer rather than by bulk dominated recombination losses. These findings are important for developing strategies how to further enhance the V of CHNHPbBr-based solar cells.
Keywords: CH3NH3PbBr3 solar cells; interface materials based losses; nonradiative recombination losses; open-circuit voltage

Exploring the Stability of Novel Wide Bandgap Perovskites by a Robot Based High Throughput Approach - Chen, Shi; Hou, Yi; Chen, Haiwei; Tang, Xiaofeng; Langner, Stefan; Li, Ning; Stubhan, Tobias; Levchuk, Ievgen; Gu, Ening; Osvet, Andres; Brabec, Christoph (Advanced Energy Materials, 2017)
Currently, lead-based perovskites with mixed multiple cations and hybrid halides are attracting intense research interests due to their promising stability and high efficiency. A tremendous amount of 3D and 2D perovskite compositions and configurations are causing a strong demand for high throughput synthesis and characterization. Furthermore, wide bandgap (≈1.75 eV) perovskites as promising top-cell materials for perovskite–silicon tandem configurations require the screening of different compositions to overcome photoinduced halide segregation and still yielding a high opencircuit voltage (Voc). Herein, a home-made high throughput robot setup is introduced performing automatic perovskite synthesis and characterization. Subsequently, four kinds of compositions (i.e., cation mixtures of Cs–methylammonium (MA), Cs– formamidinium (FA), MA–FA, and FA–MA) with an optical bandgap of ≈1.75 eV are identified as promising device candidates. For Cs–MA and Cs–FA films it is found that the Br–I phase segregation indeed can be overcome. Moreover, Cs–MA, MA–FA, and Cs–FA based devices exhibit an average Voc of 1.17, 1.17, 1.12 V, and their maximum values approached 1.18, 1.19, 1.14 V, respectively, which are among the highest Voc (≈1.2 V) values for ≈40% Br perovskite. These findings highlight that the high throughput approach can effectively and efficiently accelerate the invention of novel perovskites for advanced applications.

Exploring the Steric Hindrance of Alkylammonium Cations in the Structural Reconfiguration of Quasi-2D Perovskite Materials Using a High-throughput Experimental Platform - Zhang, Jiyun; Wu, Jianchang; Langner, Stefan; Zhao, Baolin; Xie, Zhiqiang; Hauch, Jens; Afify, Hany A.; Barabash, Anastasia; Luo, Junsheng; Sytnyk, Mykhailo; Meng, Wei; Zhang, Kaicheng; et al. (Advanced Functional Materials, 2022)
Reduced-dimensional (2D or quasi-2D) perovskites have recently attracted considerable interest due to their superior long-term stability. The nature of the intercalating cations plays a key role in determining the physicochemical properties and stability of the quasi-2D perovskites. Here, the thermal stability of a series of 2D Ruddlesden−Popper (RP) perovskites is studied using seven types of intercalating cations with increasing linear carbon-chain length from ethylammonium (EA) to n-dodecylammonium (DA) through a high-throughput platform. The results show that long-chain cations in quasi-2D perovskite films lead to strong steric hindrance between adjacent perovskite domains, thus suppressing Ostwald ripening during the thermal-aging process. For short-chain cations, increased-dimensional phase redistribution during the aging period is observed, which can benefit a concomitant regeneration of the 3D/3D-like perovskite phases. The impact of steric hindrance on structural reconfiguration and the subsequent phase redistribution in quasi-2D perovskites are systematically characterized by UV–vis absorption spectra, photoluminescence spectra, and X-ray diffraction patterns. Due to the steric hindrance effect, an optimal chain length is found to maximize film stability by balancing the water/oxygen resistance and increased-dimensional phase redistribution. This work provides new insight into the thermal stability of quasi-2D perovskites.
CRIS-Team Scopus Importer:2022-09-02
Keywords: 2D perovskite materials; high-throughput platform; stability performance; steric hindrance; steric structure and reconfiguration

Extending the environmental lifetime of unpackaged perovskite solar cells through interfacial design - Chen, Haiwei; Hou, Yi; Halbig, Christian Eberhard; Chen, Shi; Zhang, Hong; Li, Ning; Guo, Fei; Tang, Xiaofeng; Gasparini, Nicola; Levchuk, Ievgen; Kahmann, Simon; Ramírez Quiroz, César Omar; et al. (Journal of Materials Chemistry A, 2016)
Solution-processed oxo-functionalized graphene (oxo-G) is employed to substitute hydrophilic PEDOT:PSS as an anode interfacial layer for perovskite solar cells. The resulting devices exhibit a reasonably high power conversion efficiency (PCE) of 15.2% in the planar inverted architecture with oxo-G as a hole transporting material (HTM), and most importantly, deploy the full open-circuit voltage (V) of up to 1.1 V. Moreover, oxo-G effectively slows down the ingress of water vapor into the device stack resulting in significantly enhanced environmental stability of unpackaged cells under illumination with 80% of the initial PCE being reached after 500 h. Without encapsulation, ∼60% of the initial PCE is retained after ∼1000 h of light soaking under 0.5 sun and ambient conditions maintaining the temperature beneath 30 °C. Moreover, the unsealed perovskite device retains 92% of its initial PCE after about 1900 h under ambient conditions and in the dark. Our results underpin that controlling water diffusion into perovskite cells through advanced interface engineering is a crucial step towards prolonged environmental stability.
Keywords: Engineering controlled terms: Cell engineering; Conducting polymers; Open circuit voltage; Perovskite; Slow light; Solar cells Environmental stability; Functionalized graphene; High power conversion; Hole-transporting materials; Interface engineering; Interfacial design; Inverted architectures; Solution-processed Engineering main heading: Perovskite solar cells

Extracting and shaping the light of OLED devices - Riedel, Daniel; Dlugosch, Julian; Wehlus, Thomas; Brabec, Christoph (Proceedings of SPIE, 2015)
Before the market entry of organic light emitting diodes (OLEDs) into the field of general illumination can occur, limitations in lifetime, luminous efficacy and cost must be overcome. Additional requirements for OLEDs used for general illumination may be imposed by workplace glare reduction requirements, which demand limited luminance for high viewing angles. These requirements contrast with the typical lambertian emission characteristics of OLEDs, which result in the same luminance levels for all emission angles. As a consequence, without additional measures glare reduction could limit the maximum possible luminance of lambertian OLEDs to relatively low levels. However, high luminance levels are still desirable in order to obtain high light output. We are presenting solutions to overcome this dilemma. Therefore this work is focused on light-shaping structures for OLEDs with an internal light extraction layer. Simulations of beam-shaping structures and shapes are presented, followed by experimental measurements to verify the simulations of the most promising structures. An investigation of the loss channels has been carried out and the overall optical system efficiency was evaluated for all structures. The most promising light shaping structures achieve system efficiencies up to 80%. Finally, a general illumination application scenario has been simulated. The number of OLEDs needed to illuminate an office room has been deduced from this scenario. By using light-shaping structures for OLEDs, the number of OLEDs needed to reach the mandatory illuminance level for a workplace environment can be reduced to one third compared to lambertian OLED
Keywords: Organic light emitting diodes; Simulations; Beam shaping; Luminous efficacy; Optical systems

Fabrication, charge carrier transport, and application of printable nanocomposites based on indium tin oxide nanoparticles and conducting polymer 3,4-ethylenedioxythiophene/polystyrene sulfonic acid - Maksimenko, Ilja; Kilian, Daniel; Mehringer, Christian; Voigt, Michael; Peukert, Wolfgang; Wellmann, Peter (Journal of Applied Physics, 2011)
Printable transparent hybrid composites consisting of indium tin oxide (In2O3:Sn; ITO) nanoparticles and conducting polymer 3,4-polyethylenedioxythiophene (PEDOT) as matrix material were developed. The basic idea is to fill up the pores of the highly porous nanoparticulate ITO network to improve the interparticle contact and hence the conductivity of printed ITO thin films. Ready-to-use and stable aqueous dispersions were fabricated starting from ITO nanoparticles and aqueous formulation of conducting PEDOT and polystyrene sulfonic acid (PSS). This report presents and discusses key factors to obtain stable ITO-PEDOT dispersions with different mixing ratios and their application for printable devices as transparent electrode material. It was found that the f-potential value is crucial for preparation of stable dispersions. Electrical and optical properties of the hybrid ITO-PEDOT coatings were analyzed. Temperature dependent resistivity measurements reveal that conduction occurs by fluctuation induced tunneling. Transparent and conducting nanocomposite layers with a conductivity as high as 132 X1cm1 were fabricated by a low-temperature (T¼130 C) and entirely vacuum-free process. An all-printed electroluminescent lamp on a flexible substrate was realized as a demonstrator showing the applicability of such coatings for voltage-driven optoelectronic devices.<br

Fabrication of Bariumtrisulphide Thin Films as Precursors for Chalcogenide Perovskites - Freund, Tim; Cicconi, Maria Rita; Wellmann, Peter (physica status solidi (b), 2022)
Chalcogenide perovskites are a promising and novel class of materials in the fields of solar cells and related subjects. However, the synthesis of thin films of these materials still is troublesome. This work attempts to utilize a phase in the Ba-S phase system with low melting point, namely, BaS3, for the thin-film synthesis of BaZrS3. The successful synthesis of BaS3 thin films is presented and confirmed by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Raman analysis. The microstructure of the synthesized BaS3 thin films shows defects and cracks and therefore needs further optimization for the use for BaZrS3 thin-film synthesis. However, the successful synthesis of BaS3 thin films is potentially a great step toward a facile BaZrS3 thin-film synthesis.
CRIS-Team WoS Importer:2022-06-17

Fabrication of broadband antireflective sub-wavelength structures on fluorescent SiC - Ou, Yiyu; Jokubavicius, Valdas; Kaiser, Michl; Wellmann, Peter; Linnarsson, Margareta K.; Yakimova, Rositsa; Syväjärvi, Mikael; Ou, Haiyan (Materials Science Forum, 2013)
Surface nanocones on 6H-SiC have been developed and demonstrated as an effective method of enhancing the light extraction efficiency from fluorescent SiC layers. The surface reflectance, measured from the opposite direction of light emission, over a broad bandwidth range is significantly suppressed from 20.5% to 1.0 % after introducing the sub-wavelength structures. An omnidirectional light harvesting enhancement (>91%), is also achieved which promotes fluorescent SiC as a good candidate of wavelength converter for white light-emitting diode
Keywords: Fluorescent SiC; Nanostructures fabrication; Photoluminescence; donor-acceptor-pair emission

Fabrication of SiC-on-Insulator (SiCOI) Layers by Chemical Vapor Deposition of 3C-SiC on Si-in-Insulator Substrates at Low Deposition Temperatures of 1120 °C - Steiner, Johannes; Schultheiß, Jana; Wang, Shouzhong; Wellmann, Peter (Crystals, 2023)
Compared to bulk silicon carbide (SiC) wafers, SiC-on-insulator (SiCOI) substrates enable new device designs of electronic switches as well as novel photonic applications. One application is a micro-resonator for the usage in a Kerr frequency comb. For SiCOI substrates, a deposition temperature below 1200 °C is advisable due to stability reasons of the buried oxide layer during chemical vapor deposition (CVD) process conditions. To create 3C-SiC-on-insulator layers, a cold-wall CVD reactor was utilized, with propane and silane as the sources for carbon and silicon, respectively. To improve the cracking of the carbon source gas at low temperatures, the inner setup of the utilized cold-wall CVD reactor was changed to a non-water-cooled system. The change of the inner reactor setup was investigated numerically, and the grown epitaxial layers were characterized by Raman, EDX, SEM-imaging and XRD spectroscopy. We demonstrate successful deposition of 3C-SiC epitaxial layer substrates at temperatures below 1200 °C without delamination on SOI.
CRIS-Team Scopus Importer:2023-12-08
Keywords: chemical vapor deposition; COMSOL Multiphysics; cubic silicon carbide; photonic applications; silicon-on-insulator

Fabrication, Optical Modeling, and Color Characterization of Semitransparent Bulk-Heterojunction Organic Solar Cells in an Inverted Structure - Ameri, Tayebeh; Dennler, Gilles; Waldauf, Christoph; Azimi, Hamed; Seemann, Andrea; Forberich, Karen; Hauch, Jens; Scharber, Markus; Hingerl, Kurt; Brabec, Christoph (Advanced Functional Materials, 2010)
Semitransparent inverted organic photodiodes are fabricated with a Baytron PH500 ethylene-glycol layer/silver grid as the top electrode. Reasonable performances are obtained under both rear- and front-side illumination and efficiencies up to 2% are achieved. Some light is shed on visual prospects through optical simulations for a semitransparent device of poly(3-hexylthiophene) (P3HT) and the C60 derivative 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C71 (PC70BM) in the inverted structure. These calculations allow the maximum efficiency achievable to be predicted for semitransparent cells based on P3HT:PC70BM versus the transparency perception for a human eye. The simulations suggest that low-bandgap materials such as poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) have a better potential for semitransparent devices. In addition, the color range recognized by the human eye is predicted by the optical simulation for some semitransparent devices including different active layers.

Facet-Dependent Surface Trap States and Carrier Lifetimes of Silicon - Tan, Chih Shan; Zhao, Yicheng; Guo, Rong Hao; Chuang, Wei Tsung; Chen, Lih Juann; Huang, Michael H. (Nano Letters, 2020)
The facet-dependent electrical conductivity properties of silicon wafers result from significant band structure differences and variations in bond length, bond geometry, and frontier orbital electron distribution between the metal-like and semiconducting planes of silicon. To further understand the emergence of conductivity facet effects, electrochemical impedance measurements were conducted on intrinsic Si 100, 110, and 111 wafers. The attempt-to-escape frequency, obtained from temperature-dependent capacitance versus applied frequency curves, and other parameters derived from typical semiconductor property measurements were used to construct a diagram of the trap energy level (Et) and the amount of trap states Nt(Et). The trap states are located 0.61-0.72 eV above the silicon conduction band. Compared to 100 and 110 wafers, Si 111 wafer shows far less densities of trap states over the range of -0.2 to 2 V. Since these trap states inhibit direct electron excitation to the conduction band, the 111 wafer having much fewer trap states presents the best electrical conductivity property. Impedance data also provide facet-specific carrier lifetimes. The 111 surface gives consistently the lowest carrier lifetime, which reflects its high electrical conductivity. Lastly, ultraviolet photoelectron spectra and diffuse reflectance spectra were taken to obtain Schottky barriers between Ag and contacting Si wafers. The most conductive 111 surface presenting the largest Schottky barrier means the degrees of surface band bending used to explain facet-dependent electrical behaviors cannot be reliably attained this way.
CRIS-Team Scopus Importer:2020-03-10
Keywords: carrier lifetime; facet-dependent properties; impedance measurements; silicon; trap states

Facile Fabrication of Superhydrophobic and Eco-Friendly Poly(lactic acid) Foam for Oil-Water Separation via Skin Peeling - Wang, Xiaolong; Pan, Yamin; Liu, Xianhu; Liu, Hu; Li, Ning; Liu, Chuntai; Schubert, Dirk W.; Shen, Changyu (ACS Applied Materials and Interfaces, 2019)
Superhydrophobic polymer foams are a good candidate for oil absorption because of their lightweight and tunable porosity and have promising applications in the long-term application of oil-water separation. However, developing a facile and green strategy to fabricate pure polymer foams with superhydrophobicity and eco-friendliness for large-scale oil-water separation remains a challenge. Here, a facile template-free water-assisted thermally impacted phase separation approach combined with skin peeling for the fabrication of superhydrophobic and eco-friendly pure poly(lactic acid) (PLA) foam for oil-water separation is proposed for the first time. The PLA foam with special micro- and nanostructures possesses a water contact angle of 151°, and the maximum saturated adsorption capacity is 31.5 g/g. More importantly, during the continuous oil-water pumping experiment, the foam has an efficiency of 98% and could maintain for more than 15 h, showing a promising prospect for cleaning large-scale oil pollution.
CRIS-Team Scopus Importer:2019-05-02
Keywords: Eco-friendly; Oil-water separation; Poly(lactic acid); Polymer foam; Recyclability; Superhydrophobicity

Facile synthesis and photovoltaic applications of a new alkylated bismethano fullerene as electron acceptor for high open circuit voltage solar cells - Baran, Derya; Erten-Ela, Sule; Kratzer, Andreas; Ameri, Tayebeh; Brabec, Christoph; Hirsch, Andreas (RSC Advances, 2015)
It is crucial to control the lowest unoccupied molecular orbital (LUMO) of electron accepting materials for producing efficient charge transfer in bulk heterojunction (BHJ) solar cells. Due to their high LUMO level, soluble bis-adducts of C60 are of high interest for improving the Voc in BHJ solar cells. In this work, we have developed a novel bis-4-propylpentyl[6,6]methanofullerene bis-adduct, NCBA, using a alkyl solubilizing group. The optoelectronic, electrochemical and photovoltaic properties of this bis-product are investigated. NCBA is successfully applied as the electron acceptor with poly(3-hexylthiophene) (P3HT) in a BHJ solar cell showing a high Voc of 0.73 V.
Keywords: Engineering controlled terms: Charge transfer; Heterojunctions; Molecular orbitals; Open circuit voltage; Solar power generation Bulk heterojunction (BHJ); Electron acceptor; Electron-accepting; Lowest unoccupied molecular orbital; Methanofullerenes; Photovoltaic applications; Photovoltaic property; Poly-3-hexylthiophene Engineering main heading: Solar cells

Facile synthesis and post-processing of eco-friendly, highly conductive copper zinc tin sulphide nanoparticles - Ahmad, Rameez; Distaso, Monica; Azimi, Seyed Hamed; Brabec, Christoph; Peukert, Wolfgang (Journal of Nanoparticle Research, 2013)
Cu2ZnSnS4 (CZTS) nanoparticles have shown promising properties to be used as an energy harvesting material. They are usually synthesised under inert atmosphere or vacuum, whereas the subsequent step of film formation is carried out under an atmosphere of sulphur and/or Sn in order to avoid the decomposition of CZTS nanoparticles into binary and ternary species as well as the formation of the corresponding oxides. In the present paper we show that both the synthesis of CZTS nanoparticles and the film formation from the corresponding suspension can be considerably simplified. Namely, the synthesis can be carried out without controlling the atmosphere, whereas during the film annealing a nitrogen atmosphere is sufficient to avoid the depletion of the CZTS kesterite phase. Furthermore, an integrated approach including in-depth Raman analysis is developed in order to deal with the challenges associated with the characterization of CZTS nanoparticles in comparison to bulk systems. The formation of competitive compounds during the synthesis such as binary and ternary sulphides as well as metal oxides nanoparticles is discussed in detail. Finally, the as-produced films have ten times higher conductivity than the state of the art.
Keywords: By-products; Defects; Kesterite; Raman spectroscopy; Stannite CZTS nanoparticles; Thermodynamic study

Failure classification of defective PV Modules based on maximum power point analysis - Fecher, Frank; Pickel, Tobias; Buerhop-Lutz, Claudia; Camus, Christian; Brabec, Christoph (32nd European Photovoltaic Solar Energy Conference and Exhibition, 2016)
Photovoltaic (PV) modules are often affected by defects caused by transport and installation or by field degradation due to environmental conditions. If a power reduction is observed in the inverter data, a detailed error cause analysis is often very cost-intensive even when using imaging methods like thermography or electroluminescence. We present a method to classify the defect type of PV modules only by evaluating the maximum power output (Pmpp) for different irradiances. Thereby, low parallel resistance, high series resistance and broken cells can be distinguished from each other. Simulations and consistent explanations confirm the experimental findings. The method works particularly well for parallel resistance problems like potential induced degradation (PID). Thus, this failure type can easily be diagnosed in modules. The method should also be applicable to data of module strings and to thermography-based failure analysis in field which will be investigated in the future.
Keywords: Defects; Degradation; Photovoltaic; PV Module; Simulation

Fassadenelemente mit organischer Photovoltaik - Egelhaaf, Hans-Joachim; Brabec, Christoph; Neberich, Marcel; Senguttuvan, Kaushik; Hoga, Felix; Kießling, Günther; Braun, Matthias; Bordin, Susanna; Wagner, Michael; Distler, Andreas; Feroze, Sarmad; Dentel, Arno (BWK Das Energie Fachmagazin, 2021)
In dem vom Bundesministerium für Wirtschaft und Energie (BMWi) geförderten Projekt „Fassade3“ entwickelt ein Konsortium aus akademischen und industriellen Partnern ein multifunktionales Fassadenelement mit integrierter organischer Photovoltaik (OPV). Die Fassade kann aufgrund ihrer modularen Struktur vorgefertigt und sowohl in Neu- als auch Bestandsgebäude integriert werden. Sie fungiert als Energiequelle, dient der thermischen Isolation, bietet Sonnenschutz für den Innenraum und optimiert so die Energieeffizienz des Gebäudes. Mit einfachen Mitteln lässt sich somit eine voll funktionsfähige und gleichzeitig ästhetisch ansprechende Konstruktion realisieren. Ein eigens entwickeltes Messsystem erlaubt die Echtzeit-Überwachung der Energiebilanz der Fassade. Erste Ergebnisse zum Leistungsverhältnis der OPV-Module sind vielversprechend.

Fast and Robust Detection of Solar Modules in Electroluminescence Images - Hoffmann, Mathis; Doll, Bernd; Talkenberg, Florian; Brabec, Christoph; Maier, Andreas; Christlein, Vincent (Computer Analysis of Images and Patterns, 2019)

Fatigue of low alloyed carbon steels in the HCF/VHCF-regimes - Bachmann, Jonas; Göken, Mathias; Höppel, Heinz Werner (Fatigue of Materials at Very High Numbers of Loading Cycles, 2018)
The fatigue behaviour and damage evolution in body centered cubic low alloyed steels in the high cycle and very high cycle fatigue regimes (HCF/VHCF) were in focus of this work. For this purpose, the steels C15E, C45E and C60E, with different ferritic-pearlitic microstructures were investigated. Due to the different carbon contents the ratio of ferrite to pearlite decreased from C15E to C60E. C15E mainly consist of ferrite grains. The ferrite grains deform plastically under cyclic loading. With decreasing stress amplitudes plastic deformation becomes more and more localized in particular ferrite grains. During further cyclic loading plastic deformation accumulates in those grains and finally leads to crack initiation and fatigue failure. The accumulation of irreversible plastic deformation in the ferrite grains and the strength of microstructural barriers in the vicinity of the plastically deformed grains are mainly determining the total fatigue life. In order to assess quantitatively the contribution of irreversible plastic deformation a new method was developed. By determining the dissipated energy per fatigue cycle, which was derived from the power input of the ultrasonic fatigue machine, it is possible to account for the amount of irreversibility during one loading pulse. Based on these results a prediction of the fatigue life can be made at a very early stage of the fatigue experiment. It also allows distinguishing very early whether the specimen will become a runout or if it will fail at a given amplitude. It also turned out that the interaction of localized plastic deformation with microstructural barriers in the direct vicinity is the key for understanding the occurrence of late fatigue failure. If specimens showed macroscopic crack growth and fatigue failure, critical cracks always initiated at interfaces. On the other hand, runout specimens showed some crack nuclei, but they were not able to overcome the next microstructural barrier.<br

Favorable Mixing Thermodynamics in Ternary Polymer Blends for Realizing High Efficiency Plastic Solar Cells - Gasparini, Nicola; Kahmann, Simon; Salvador, Michael Filipe; Perea, Jose Dario; Sperlich, Andreas; Baumann, Andreas; Li, Ning; Rechberger, Stefanie; Spiecker, Erdmann; Dyakonov, Vladimir; Portale, Giuseppe; Loi, Maria A.; et al. (Advanced Energy Materials, 2019)
Ternary blends with broad spectral absorption have the potential to increase charge generation in organic solar cells but feature additional complexity due to limited intermixing and electronic mismatch. Here, a model system comprising the polymers poly[5,5-bis(2-butyloctyl)-(2,2-bithiophene)-4,4-dicarboxylate-alt-5,5-2,2-bithiophene] (PDCBT) and PTB7-Th and PC70BM as an electron accepting unit is presented. The power conversion efficiency (PCE) of the ternary system clearly surpasses the performance of either of the binary systems. The photophysics is governed by a fast energy transfer process from PDCBT to PTB7-Th, followed by electron transfer at the PTB7-Th:fullerene interface. The morphological motif in the ternary blend is characterized by polymer fibers. Based on a combination of photophysical analysis, GIWAXS measurements and calculation of the intermolecular parameter, the latter indicating a very favorable molecular affinity between PDCBT and PTB7-Th, it is proposed that an efficient charge generation mechanism is possible because PTB7-Th predominantly orients around PDCBT filaments, allowing energy to be effectively relayed from PDCBT to PTB7-Th. Fullerene can be replaced by a nonfullerene acceptor without sacrifices in charge generation, achieving a PCE above 11%. These results support the idea that thermodynamic mixing and energetics of the polymer–polymer interface are critical design parameter for realizing highly efficient ternary solar cells with variable electron acceptors</stron
Keywords: FRET; high efficiency; ternary organic solar cells; mixing thermodynamics; photophysics

Feedstock recharging during directional solidification of silicon ingots for PV applications - Beier, Maximilian; Trempa, M.; Seebeck, Jan; Reimann, C.; Wellmann, Peter; Gründig-Wendrock, B.; Friedrich, J.; Dadzis, K.; Sylla, L.; Richter, T. (Proceedings of the 29th EU PVSEC conference, 2015)
Directional solidification (DS) is a well-established crystallization technology to produce polycrystalline or quasi-mono crystalline silicon ingots for photovoltaic applications. Before the crystallization process the silica crucible is charged with irregular shaped silicon feedstock typically resulting in a filling degree of 50 to 60%. Hence, the grown silicon ingot is only about the half of the available crucible height or volume, respectively. The upper part of the crucible cannot be used for crystallization which means considerable yield losses. One approach to overcome this problem is the recharging of new silicon feedstock (solid or liquid state) into the melt during crystallization. In this work the effects of the recharging processes on the crystal growth behavior and the material properties were investigated. At the beginning the immersion behavior of the silicon feedstock into the silicon melt was simulated by model experiments where polyethylene granules were dropped into water. Afterwards some growth experiments in a modified G1-DS-furnace were carried out. The recharging process was done with 10 kg of different feedstock types leading to a 60% increase of ingot height from 130 to 210 mm. After crystallization the grain structure and the specific resistivity of the silicon ingots were investigated. The results show that the contact of the recharged feedstock particles with the solid liquid interface has necessarily to be avoided to grow high quality silicon ingots by this technology. Additionally it could be demonstrated that recharging of undoped feedstock during the crystallization process has the potential to flat the resistivity gradient over the ingot height.<br
Keywords: Crystalline Silicon; Directional Solidification; Recharging

Field dependent carrier dynamics and charged excitons in InAs self-assembled quantum dots - Schmidt, K.H.; Kunze, U.; Medeiros-Ribeiro, G.; Garcia, J.M.; Wellmann, Peter; Petroff, P.M. (Physica E-Low-Dimensional Systems & Nanostructures, 1998)
We have used photocapacitance, photocurrent and photoluminescence spectroscopy to study the field-dependent dynamics and radiative recombination of optically excited electron-hole pairs in InAs self-assembled quantum dots (QDs) under various charging conditions. In the investigated field region the excitons relax into the ground state before tunneling or radiative recombination takes place. At high internal fields electrons and holes tunnel out of the QDs while at low fields the excitons recombine in the dot. In the low-field regime a red shift of the QD ground slate photoluminescence is observed when the QDs are loaded with electrons. A decrease in the overall intensity indicates a lower oscillator strength of charged excitons in InAs self-assembled QDs. Field effects being responsible for the observed energy shift can be excluded since the energetic position of the ground-state transition remains constant at high fields. (C) 1998 Elsevier Science B.V. All rights reserved.
Keywords: InAs quantum dots; charged excitons; carrier dynamics; field effects

Fine-tuning of the chemical structure of photoactive materials for highly efficient organic photovoltaics - Fan, Baobing; Du, Xiaoyan; Liu, Feng; Zhong, Wenkai; Ying, Lei; Xie, Ruihao; Tang, Xiaofeng; An, Kang; Xin, Jingming; Li, Ning; Ma, Wei; Brabec, Christoph; et al. (Nature Energy, 2018)
The performance of organic photovoltaics is largely dependent on the balance of short-circuit current density (JSC) and open-circuit voltage (VOC). For instance, the reduction of the active materials’ optical bandgap, which increases the JSC, would inevitably lead to a concomitant reduction in VOC. Here, we demonstrate that careful tuning of the chemical structure of photoactive materials can enhance both JSC and VOC simultaneously. Non-fullerene organic photovoltaics based on a well-matched materials combination exhibit a certified high power conversion efficiency of 12.25% on a device area of 1 cm2. By combining Fourier-transform photocurrent spectroscopy and electroluminescence, we show the existence of a low but non-negligible charge transfer state as the possible origin of VOC loss. This study highlights that the reduction of the bandgap to improve the efficiency requires a careful materials design to minimize non-radiative VOC losses. © 2018, The Author(s), under exclusive licence to Springer Nature Limite
Keywords: Active material; Charge transfer state; Concomitant reduction; High power conversion; Materials design; Organic photovoltaics; Photoactive materials; Photocurrent spectroscopy

First Year of Smart Metering with a High Time Resolution - Realistic Self-Sufficiency Rates for Households with Solar Batteries - Stegner, Christoph; Bogenrieder, Josef; Luchscheider, Philipp; Brabec, Christoph (Energy Procedia, 2016)
Measured data from distribution grids with a high time resolution is scarce although it is where most volatile power profiles occur. Electrical storage systems (ESS) can mitigate the imbalance of generation and demand. In this study smart meter data with a temporal resolution of 15 s is analyzed and an algorithm described, that allows identifying differently oriented generator in mixed PV plants. Various self-consumption scenarios are simulated with different setups and temporal resolution. The calculated self-sufficiency rates lead to recommendations for the dimensioning and give precise values for the correction of key parameters from simulations if data is not available in high temporal resolution. © 2016 The Authors. Published by Elsevier Ltd.
Keywords: dimensioning; PV battery systems; PV simulation; residential smart meter; self-consumption; temporal resolution

Flexible and highly segmented OLED for automotive applications - Bechert, Hermann; Wittmann, Sebastian; Brabec, Christoph; Wehlus, Thomas (Proceedings Volume 10687, Organic Electronics and Photonics: Fundamentals and Devices; 106870Q, 2018)
Today OLEDs are established light-sources for automotive rear-lights. OLEDs having a small number of segments can be found in various cars and are about to spread further. Beyond this state-of-the-art OLEDs being flexible as well as featuring a higher number of segments are desired by OEMs. Unfortunately conventional display approaches like passive and active matrix displays are struggling to deliver the high luminance and fill factor required for automotive applications and are therefore unable to fulfill the requirements by the automotive lighting industry. In this work we are going to present our approach on flexible and highly segmented OLED applications for Automotive to overcome this problem. An investigation of a novel device concept is demonstrated, as well as details on our substrate technology development, encapsulation and electronic/driving schemes. A strong focus has been put on the possibility to use standard lithography for substrate creation to have, if possible, no impact on existing supply chains and a maximum of reliability due to the use of well-known processes. The core concept for flexible and highly segmented OLED devices is derived from this processes. Challenges that occurred during the manufacturing of the substrates and devices are described in detail as well as solutions to circumvent these unexpected problems. Measurements of OLED key parameters are presented together with visual impressions of the devices. Driving schemes and electronics needed to control the OLED segments are introduced in short to complete the study of the overall concept of flexible and highly segmented OLEDs for automotive application
Keywords: segmentation; OLED; rear-light; flexible; automotive

Flexible organic tandem solar modules: A story of up-scaling - Spyropoulos, Georgios; Kubis, Peter; Li, Ning; Lucera, Luca; Salvador, Michael Filipe; Baran, Derya; Machui, Florian; Ameri, Tayebeh; Voigt, Monika; Brabec, Christoph (Organic Photovoltaics XV, 2014)
The competition in the field of solar energy between Organic Photovoltaics (OPVs) and several Inorganic Photovoltaic technologies is continuously increasing to reach the ultimate purpose of energy supply from inexpensive and easily manufactured solar cell units. Solution-processed printing techniques on flexible substrates attach a tremendous opportunity to the OPVs for the accomplishment of low-cost and large area applications. Furthermore, tandem architectures came to boost up even more OPVs by increasing the photon-harvesting properties of the device. In this work, we demonstrate the road of realizing flexible organic tandem solar modules constructed by a fully roll-to-roll compatible processing. The modules exhibit an efficiency of 5.4% with geometrical fill factors beyond 80% and minimized interconnection-resistance losses. The processing involves low temperature (<70 °C), coating methods compatible with slot die coating and high speed and precision laser patterning.
Keywords: Flexible solar cells; Laser patterning; Organic solar modules; Organic tandem solar cells; Solution-processing

Flexible organic tandem solar modules with 6% efficiency: combining roll-to-roll compatible processing with high geometric fill factors - Spyropoulos, Georgios; Kubis, Peter; Li, Ning; Baran, Derya; Lucera, Luca; Salvador, Michael Filipe; Ameri, Tayebeh; Voigt, Monika; Krebs, F. C.; Brabec, Christoph (Energy and Environmental Science, 2014)
Organic solar cell technology bears the potential for high photovoltaic performance combined with truly low-cost, high-volume processing. Here we demonstrate organic tandem solar modules on flexible substrates fabricated by fully roll-to-roll compatible processing at temperatures <70 °C. By using ultrafast laser patterning we considerably reduced the “dead area” of the modules and achieved geometric fill factors beyond 90%. The modules revealed very low interconnection-resistance compared to the single tandem cells and exhibited a power conversion efficiency of up to 5.7%. Bending tests performed on the modules suggest high mechanical resilience for this type of device. Our findings inform concrete steps towards high efficiency photovoltaic applications on curved, foldable and moving surfaces.
Keywords: Fill factor; Roll to Roll; Solar module GEOBASE Subject Index: photovoltaic system; resilience; solar power; volume

Flexible Photocatalytic Electrode Using Graphene, Non-noble Metal, and Organic Semiconductors for Hydrogen Evolution Reaction - Kondo, Kohei; Watanabe, Yusuke; Kuno, Junya; Ishii, Yosuke; Kawasaki, Shinji; Kato, Masashi; Kalita, Golap; Hattori, Yoshiyuki; Mashkov, Oleksandr; Sytnyk, Mykhailo; Heiß, Wolfgang (Energy Technology, 2021)
Two kinds of visible light-responsible organic semiconductors (epindolidione [EPI] and fluorinated EPI [2F-EPI]) are synthesized. The solar hydrogen evolution photocatalytic electrode properties of the organic semiconductors are investigated and the heterostructure effect caused by manipulating the order of the deposition of 2F-EPI and EPI is found, which increased the photoresponse current by reducing the carrier recombination of photoexcited electrons and holes. In addition, it is found that the deposition of Ni metal on the organic semiconductors further enhanced the photoresponse current and increased the durability of the organic semiconductor photocatalyst. Finally, a flexible photocatalytic electrode using graphene, organic semiconductors, and non-noble metal cocatalyst for solar hydrogen generation is prepared. A transparent flexible electric conductive film is prepared by transfer of a graphene sheet on the polymer film. The graphene electrode is coated by two kinds of organic semiconductors layer by layer to reduce recombination of photoexcited electrons and holes. Ni metal particles are deposited on the surface of the organic semiconductor layer as a cocatalyst to improve the photocatalytic property and durability of organic semiconductors. A clear photoresponse current (about 4 mu A cm(-2)) of the flexible photocatalytic electrode under the simulated solar light (AM 1.5 G, 100 mW cm(-2)) is observed.
CRIS-Team WoS Importer:2021-06-04

Flexible sample cell for real-time GISAXS, GIWAXS and XRR: design and construction - Berlinghof, Marvin; Bär, Christian; Haas, D.; Bertram, F.; Langner, Stefan; Osvet, Andres; Chumakov, A.; Will, Johannes; Schindler, Torben; Zech, Tobias; Brabec, Christoph; Unruh, Tobias (Journal of Synchrotron Radiation, 2018)
Since the properties of functional materials are highly dependent on their specific structure, and since the structural changes, for example during crystallization, induced by coating and annealing processes are significant, the study of structure and its formation is of interest for fundamental and applied science. However, structure analysis is often limited to ex situ determination of final states due to the lack of specialized sample cells that enable real-time investigations. The lack of such cells is mainly due to their fairly complex design and geometrical restrictions defined by the beamline setups. To overcome this obstacle, an advanced sample cell has been designed and constructed; it combines automated doctor blading, solvent vapor annealing and sample hydration with real-time grazing-incidence wide- and small-angle scattering (GIWAXS/GISAXS) and X-ray reflectivity (XRR). The sample cell has limited spatial requirements and is therefore widely usable at beamlines and laboratory-scale instruments. The cell is fully automatized and remains portable, including the necessary electronics. In addition, the cell can be used by interested scientists in cooperation with the Institute for Crystallography and Structural Physics and is expandable with regard to optical secondary probes. Exemplary research studies are presented, in the form of coating of P3HT:PC61PM thin films, solvent vapor annealing of DRCN5T:PC71BM thin films, and hydration of supported phospholipid multilayers, to demonstrate the capabilities of the in situ cell.
Keywords: in situ; GIWAXS; GISAXS; XRR; thin film

Flexible Solar Cells - Maisch, Philipp; Lucera, Luca; Egelhaaf, Hans-Joachim; Brabec, Christoph (Flexible Carbon-based Electronics, 2018)
This third volume in the Advanced Nanocarbon Materials series covers the topic of flexible electronics both from a materials and an applications perspective. Comprehensive in its scope, the monograph examines organic, inorganic and composite materials with a section devoted to carbon-based materials with a special focus on the generation and properties of 2D materials. It also presents carbon modifications and derivatives, such as carbon nanotubes, graphene oxide and diamonds. In terms of the topical applications covered these include, but are not limited to, flexible displays, organic electronics, transistors, integrated circuits, semiconductors and solar cells. These offer perspectives for today?s energy and healthcare challenges, such as electrochemical energy storage and wearable devices. Finally, a section on fundamental properties and characterization approaches of flexible electronics rounds off the book. Each contribution points out the importance of the structure-function relationship for the target-oriented fabrication of electronic devices, enabling the design of complex component

Flexible top-emitting OLEDs for lighting: Bending limits - Schwamb, Philipp; Reusch, Thilo; Brabec, Christoph (Organic Light Emitting Materials and Devices XVII, 2013)
Flexible OLED light sources have great appeal due to new design options, being unbreakable and their low weight. Top-emitting OLED device architectures offer the broadest choice of substrate materials including metals which are robust, impermeable to humidity, and good thermal conductors making them promising candidates for flexible OLED device substrates. In this study, we investigate the bending limits of flexible top-emitting OLED lighting devices with transparent metal electrode and thin film encapsulation on a variety of both metal and plastic foils. The samples were subjected to concave and convex bending and inspected by different testing methods for the onset of breakdown for example visible defects and encapsulation failures. The critical failure modes were identified as rupture of the transparent thin metal top electrode and encapsulation for convex bending and buckling of the transparent metal top electrode for concave bending. We investigated influences from substrate material and thickness and top coating thickness. The substrate thickness is found to dominate bending limits as expected by neutral layer modeling. Coating shows strong improvements for all substrates. Bending radii <15mm are achieved for both convex and concave testing without damage to devices including their encapsulation. © 2013 SPIE.
Keywords: Bending; Flexible; Organic light-emitting diode; Thin film encapsulation; Transparent metal electrode

Flow stability, convective heat transfer and chemical reactions in ammonothermal autoclaves—insights by in situ measurements of fluid temperatures - Schimmel, Saskia; Kobelt, Ines; Heinlein, Lukas; Kimmel, Anna-Carina; Steigerwald, Thomas; Schlücker, Eberhard; Wellmann, Peter (Crystals, 2020)
A variety of functional nitride materials, including the important wide bandgap semiconductor GaN, can be crystallized in exceptionally good structural quality by the ammonothermal method. However, the further development of this method is hindered by a lack of access to internal process parameters including fluid temperatures, flow stability and reaction kinetics. Internal temperature measurements are thus introduced as a tool for in situ monitoring of fluid flow stability in ammonothermal reactors as well as chemical reactions associated with enthalpy changes. The temperature change of an internal thermocouple is studied numerically in order to estimate possible errors due to heat conduction along thermocouples as well as due to their heat capacity. Results from otherwise identical experiments conducted with air at ambient pressure and ammonothermal reaction medium, respectively, are compared. The comparison indicates that internal temperature distributions during ammonothermal growth of GaN cannot be determined by measurements using ambient pressure air instead of supercritical ammonia. Even an approximate determination is not feasible, given that the internal temperature gradients differ by a factor of seven, and that the Grashof-and Rayleigh numbers differ by approximately four orders of magnitude. Most importantly, convective heat transfer by supercritical ammonia is found to greatly influence the temperature distribution inside the reaction chamber and its walls, suggesting that it probably needs to be taken into account in numerical simulations of the global thermal field of ammonothermal reactors.
CRIS-Team Scopus Importer:2020-08-28
Keywords: Ammonothermal; Bulk crystal growth; Convective heat transfer; Fluid flow; GaN; In situ monitoring; Natural convection; Reaction monitoring; Solvothermal

Fluorescent SiC as a new material for white LEDs - Syväjärvi, Mikael; Müller, Julian; Sun, J. W.; Grivickas, V.; Ou, Yiyu; Jokubavicius, V.; Hens, Philip; Kaiser, Michl; Ariyawong, K.; Gulbinas, K.; Liljedahl, R.; Linnarsson, M. K.; et al. (Physica Scripta, 2012)
Current III-V-based white light-emitting diodes (LEDs) are available. However, their yellow phosphor converter is not efficient at high currents and includes rare-earth metals, which are becoming scarce. In this paper, we present the growth of a fluorescent silicon carbide material that is obtained by nitrogen and boron doping and that acts as a converter using a semiconductor. The luminescence is obtained at room temperature, and shows a broad luminescence band characteristic of donor-to-acceptor pair recombination. Photoluminescence intensities and carrier lifetimes reflect a sensitivity to nitrogen and boron concentrations. For an LED device, the growth needs to apply low-off-axis substrates. We show by ultra-high-resolution analytical transmission electron microscopy using aberration-corrected electrons that the growth mechanism can be stable and that there is a perfect epitaxial relation from the low-off-axis substrate and the doped layer even when there is step-bunching.
Keywords: Silicon Carbide; SiC; Fluorescence; white LED

Fluorine Aided Stabilization of Pt Single Atoms on TiO2 Nanosheets and Strongly Enhanced Photocatalytic H2 Evolution - Wu, Si-Ming; Hwang, Imgon; Osuagwu, Benedict; Will, Johannes; Wu, Zhenni; Sarma, Bidyut Bikash; Pu, Fu-Fei; Wang, Li-Ying; Badura, Zdeněk; Zoppellaro, Giorgio; Spiecker, Erdmann; Schmuki, Patrik (ACS Catalysis, 2022)
Trapping sites in single atom (SA) catalysts are critical to the stabilization and reactivity of isolated atoms. Herein, we show that anchoring of Pt SAs on TiO2 nanosheets is strongly aided by lattice incorporated fluorine species. Tailoring the speciation of fluorine on TiO2 nanosheets is a key factor for uniform and stable dispersion of the Pt SAs and high efficiency in Pt SA co-catalyzed photocatalytic H2 production. Fluorine-stabilized uniformly dispersed Pt SAs on the (001) surface of TiO2 can provide a remarkable photocatalytic activity (a H2 production rate of 45.3 mmol h–1 mg–1 Pt for 65 mW/cm2 365 nm light). This high (maximized) efficiency can be achieved with a remarkably low loading amount of Pt SAs on TiO2 nanosheets (0.03 wt %), which is far superior to Pt nanoparticles on a TiO2 nanosheet with the same or a higher loading amount. F-stabilized Pt SAs on TiO2 nanosheets also exhibit an excellent stability in long-term photocatalytic reactions.<br

Formation and properties of nanosize ferromagnetic MnAs particles in low temperature GaAs by manganese implantation - Wellmann, Peter; Feng, J.-L; Garcia, J.M.; Petroff, P.M. (Materials Research Society Symposium - Proceedings, 1997)
The synthesis of ferromagnetic particles of the size of several nm (10… 100nm) imbedded in semiconductors is of particular interest for device applications such as magnetic sensors, switches or memories based on integrated semiconductor devices. We have investigated the formation as well as the structural and magnetic properties of MnAs nanomagnets (size ≈ 20nm) in low temperature grown GaAs (LT-GaAs). The MnAs nanomagnets which show ferromagnetism at room temperature have been synthesized using ion implantation with Mn and subsequent rapid thermal annealing (RTA). To characterize these nanomagnets, we present SQUID measurements (superconducting quantum interference device), TEM analysis (transmission electron microscopy) and EDX analysis (electron beam induced x-ray fluorescence

Formation of a Non-Thickness-Limited Titanium Dioxide Mesosponge and its Use in Dye-Sensitized Solar Cells - Kim, Dam-Hee; Lee, Kiyoung; Roy, Poulomi; Birajdar, Balaji; Spiecker, Erdmann; Schmuki, Patrik (Angewandte Chemie International Edition, 2009)
Etch a sketch: Robust TiO_2 mesoporous layers can be fabricated on Ti surfaces by a combination of non-thickness-limited anodization and selective etching. Layers more than 50 extgreekmm thick with highly regular feature and pore sizes in the range 5–10 nm can be produced (see picture, FTO=fluorine doped tin oxide). The layers are highly flexible, well-adhered, and can be used directly after appropriate annealing in efficient dye-sensitized solar cells.
Keywords: dyes/pigments; mesoporous materials; solar cells; titanates; titanium

Formation of Cu2SnSe3 from stacked elemental layers investigated by combined in situ X-ray diffraction and differential scanning calorimetry techniques - Wibowo, Rachmat Adhi; Möckel, Stefan; Yoo, Hye Sun; Hölzing, Astrid; Hock, Rainer; Wellmann, Peter (Journal of Alloys and Compounds, 2014)
Stacked elemental layers of Mo/Cu/Sn and Mo/Cu/Sn/Se were employed as samples for investigating the formation reaction of Cu-Sn intermetallic compounds as well as CuSnSe phases by in situ technique of X-ray diffraction and differential scanning calorimetry. The use of a combined in situ technique allows a real-time observation on solid-state reactions as well as any crystalline phase changes during annealing towards the crystallization of CuSnSe. It is found that Cu and Sn form intermetallic compounds of CuSn, CuSn and CuSn as the annealing temperature rises from 30 to 550 C. The reaction of Se with Cu to form a CuSe phase dominates the binary phase formation at a low annealing temperature. The annealing of a stacked Mo/Cu/Sn/Se layer suggests that only CuSn intermetallic compound directly acts as a reactant for the Cu-selenide phase formation. A SnSe phase mostly forms from a liquid-state reaction of Sn and Se above the Sn melting point. The in situ investigation also reveals a complete set of Cu-selenide peritectic decompositions of CuSe → CuSe → CuSe at 360 and 412 C. The formation of CuSnSe phase starts at 450 C as a product from a reaction between Cu Se and SnSe in a presence of liquid Se. Comparisons on the initial formation temperatures of all involved phases and on the formation pathways between CuSnSe and CuSnS are discussed as well. © 2013 Elsevier B.V. All rights reserved.
Keywords: Intermetallics; Thermoelectric materials; Solid state reactions; Phase transitions

Formation of nanoscale ferromagnetic MnAs crystallites in low-temperature grown GaAs - Wellmann, Peter; Garcia, J.M.; Feng, J.-L; Petroff, P.M. (Applied Physics Letters, 1997)
We report the formation of nanosize ferromagnetic MnAs crystallites imbedded in low-temperature grown GaAs using Mn1 ion implantation and subsequent annealing. The structural and magnetic properties of the crystallites have been characterized by transmission electron microscopy, electron beam induced x-ray fluorescence, and superconducting quantum interference device magnetometry. After an optimized thermal annealing at 750 °C, MnAs crystallites of 50 nm in size are formed. These nanomagnets show room temperature ferromagnetism. <br

Freestanding 3C-SiC grown by sublimation epitaxy using 3C-SiC templates on silicon - Hens, Philip; Müller, Julian; Wagner, Günter; Liljedahl, Rickard; Yakimova, Rositza; Spiecker, Erdmann; Wellmann, Peter; Syväjärvi, Mikael (Materials Science Forum, 2012)
In this work a new approach for the production of freestanding cubic silicon carbide (3C-SiC) in (001) orientation is presented which is based on the combination of chemical vapor deposition (CVD) and the fast sublimation growth process (FSGP). Fast homoepitaxial growth of 3C-SiC using sublimation epitaxy on a template created by CVD growth on silicon substrates allows to obtain thick freestanding material with low defect densities. Using standard silicon wafers as substrate material permits a cost efficient process and the applying of wafers with different orientations. The (001) orientation used in this work will potentially allow further heteroepitaxial growth of other cubic semiconductors, like e.g. gallium nitride (GaN). © (2012) Trans Tech Publication
Keywords: Cubic silicon carbide; Defect reduction; Heteroepitaxy; Sublimation growth

From fullerene acceptors to non-fullerene acceptors: Prospects and challenges in the stability of organic solar cells - Speller, Emily M.; Clarke, Andrew J.; Luke, Joel; Lee, Harrison Ka Hin; Durrant, James R.; Li, Ning; Wang, Tao; Wong, Him Cheng; Kim, Ji Seon; Tsoi, Wing Chung; Li, Zhe (Journal of Materials Chemistry A, 2019)
The recent emergence of non-fullerene small molecule acceptors has reinvigorated the field of organic solar cells, already resulting in significant breakthroughs in their power conversion efficiency and discovery of remarkable new science. The stability and degradation of this class of materials and devices, on the other hand, has to date received relatively less attention. Herein, we present a critical review into the fundamentally different degradation mechanisms of non-fullerene acceptors compared to fullerene acceptors, as well as the very different roles they play upon the charge carrier generation and recombination kinetics and the resulting solar cell stability. We highlight in particular the prospect of the emergence of non-fullerene acceptors in addressing several major degradation mechanisms related to the use of fullerene acceptors, in conjunction with a number of unique degradation mechanisms that only exist in non-fullerene acceptors, which would provide an important guideline for further developments toward achieving long-term stability of organic solar cells.
CRIS-Team Scopus Importer:2019-11-05

From Semiconductors to New Energy – the PV Value added Chain, Proceedings of the E-MRS ICAM IUMRS 2011 Spring Meeting - Richter, Hans; Wellmann, Peter (2011)

From thin film to bulk 3C-SiC growth: Understanding the mechanism of defects reduction - La Via, F.; Severino, A.; Anzalone, R.; Bongiorno, C.; Litrico, G.; Mauceri, M.; Schöler, Michael; Schuh, Philipp; Wellmann, Peter (Materials Science in Semiconductor Processing, 2018)
In this review the effect of the growth process on the formation of defects in the hetero-epitaxial 3C-SiC film and the possible path for defects reduction has been reported. In our analysis of the experimental data we started from the realization of the carbonization layer, the defects at the interface and in the silicon substrate, to the growth of thin and even very thick layers. The discussion has been focalized on the growth on planar blanket Si substrates without the presence of structures or specific buffer layers. Both Chemical Vapour Deposition (CVD) and Sublimation Epitaxy (SE) processes have been reported and studied in detail.
Keywords: 3S-SiC; defects; sublimation epitaxy

Front side illuminated dye-sensitized solar cells using anodic TiO2 mesoporous layers grown on FTO-glass - Lee, Kiyoung; Kim, Dam-Hee; Berger, Stefan; Kirchgeorg, Robin; Schmuki, Patrik (Electrochemistry Communications, 2012)
In the present work, we investigate the performance of anodic, self-organized TiO2 mesoporous structures (TMSs) in dye-sensitized solar cells (DSSCs) under front-side illumination conditions. In order to fabricate structures usable in a front-side (FS) configuration, TMSs were formed on FTO glass by a full anodic conversion of evaporated Ti films on the glass substrate in a glycerol/K2HPO4 electrolyte at 180 °C. The resulting mesoporous layers can be assembled to FS dye sensitized solar cells which show a thickness of only 3 extgreekmm and a remarkable efficiency of 4.34%. This is significantly higher than, for example, anodic TiO2 nanotubes of the same length even after efficiency enhancing TiCl4 treatments (3.01%). The best efficiency value for TMS-based DSSCs that we currently reached is for a 7 extgreekmm thick TMS layer, this is ≈6.82% which is highly promising for further improvements.
EAM Import::2019-03-14

FTIR study of the impact of PC[60]BM on the photodegradation of the low band gap polymer PCPDTBT under O2 environment - Dettinger, Ulf; Egelhaaf, Hans-Joachim; Brabec, Christoph; Latteyer, Florian; Peisert, Heiko; Chasse, Thomas (Chemistry of Materials, 2015)
The photodegradation of the low band gap polymer poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) during irradiation under white light (AM 1.5 conditions) has been studied in pristine polymer films as well as in blend films with [6,6]-phenyl C61 butyric acid methyl ester (PC[60]BM). In order to gain insight into the degradation process, FTIR spectroscopy has been used to follow the evolution of different subunits of the polymer and to probe the chemical product formation. In contrast to other polymers, not the alkyl side chains but the π-conjugated system is preferentially oxidized during the first stages of degradation. Furthermore, it has been shown that the subunits of the polymer backbone are differently affected by the degradation. Blending the polymer with PC[60]BM leads to a significantly larger impact on the stability of the cyclopentadiene group compared to the benzene ring of the benzothiadiazole group.
Keywords: Engineering controlled terms: Blending; Butyric acid; Conjugated polymers; Energy gap; Fourier transform infrared spectroscopy; Polymers 2; 1; 3-Benzothiadiazole; Alkyl side chains; Cyclopentadiene groups; Degradation process; FTIR spectroscopy; Low bandgap polymers; Pi-conjugated system; Pristine polymers Engineering main heading: Polymer films

Fullerene sensitized silicon for near- to mid-infrared light detection - Matt, Gebhard J.; Fromherz, Thomas; Bednorz, Mateusz; Zamiri, Saeid; Goncalves, Guillaume; Lungenschmied, Christoph; Meissner, Dieter; Sitter, Helmut; Sariciftci, N. Serdar; Brabec, Christoph; Bauer, Guenther (Advanced Materials, 2010)
A novel light-sensing scheme based on a silicon/fullerene-derivative heterojunction allows optoelectronic detection in the near- to mid-infrared (IR), which is fully compatible with complementary metal oxide semiconductor (CMOS) technology. Although silicon and the fullerene derivative do not absorb in the IR, a heterojunction of these materials absorbs and generates a photocurrent (PC) in the near- to mid-IR, presumably caused by an interfacial absorption mechanism. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fully Printed and Industrially Scalable Semitransparent Organic Photovoltaic Modules: Navigating through Material and Processing Constraints - Wachsmuth, Josua; Distler, Andreas; Liu, Chao; Heumüller, Thomas; Liu, Yang; Aitchison, Catherine M.; Hauser, Alina; Rossier, Michael; Robitaille, Amélie; Llobel, Marc Antoine; Morin, Pierre Olivier; Thepaut, Anaïs; et al. (Solar RRL, 2023)
While the power conversion efficiency (PCE) of organic photovoltaics (OPV) on small-area lab cells has rapidly increased during the last few years, the performance on module level and the availability of OPV modules on the market is still limited, primarily due to specific constraints imposed by the industrial production process. This work deals with the upscaling process of latest-generation OPV from small-area lab cells to fully solution-processed modules, which are compatible to industrial roll-to-roll (R2R) printing. This transfer is demonstrated step by step from material selection and process optimization for every single layer of the stack (photoactive layer, charge transporting layers, and solution-processed top electrode)–including long-term stability investigations (thermal and light)–to scaling up the device area by a factor of >100. Thus, a semitransparent OPV module with 10.8% PCE on 10.2 cm2 active area is achieved, which is among the highest performances for semitransparent, fully solution-processed OPV modules. The individual developments all meet the requirements for industrial R2R printing (green solvents, processing in air, annealing ≤140 °C, etc.), which ensures that both the optimized layer stack and the fabrication process are fully scalable and easily transferable to large-scale production.
CRIS-Team Scopus Importer:2023-09-22
Keywords: ambient air; organic photovoltaics (OPVs); roll-to-roll (R2R)-compatibility; semitransparent modules; solution-processing; upscaling

Fully printed flexible perovskite solar modules with improved energy alignment by tin oxide surface modification - Dong, Lirong; Qiu, Shudi; García Cerrillo, José; Wagner, Michael; Kasian, Olga; Feroze, Sarmad; Jang, Dongju; Li, Chaohui; Le Corre, Vincent Marc; Zhang, Kaicheng; Peisert, Heiko; U. Kosasih, Felix; et al. (Energy and Environmental Science, 2024)
Fully printed flexible perovskite solar cells (f-PSCs) show great potential for the commercialization of perovskite photovoltaics owing to their compatibility with high-throughput roll-to-roll (R2R) production. However, the challenge remains in the deficiency in controlling interfacial recombination losses of the functional layer, causing remarkable loss of power conversion efficiency (PCE) in industrial production. Here, a fullerene-substituted alkylphosphonic acid dipole layer is introduced between the R2R-printed tin oxide electron transport layer and the perovskite active layer to reduce the energetic barrier and to suppress surface recombination at the buried interface. The resulting f-PSCs exhibit a PCE of 17.0% with negligible hysteresis, retain 95% of their initial PCE over 3000 bending cycles and achieve a T95 lifetime of 1200 h under 1 sun and 65 °C in nitrogen atmosphere. Moreover, the fully printed flexible perovskite solar mini-modules (f-PSMs) with a 20.25 cm2 aperture area achieve a PCE of 11.6%. The encapsulated f-PSMs retain 90% of their initial PCE after 500 h damp-heat testing at 65 °C and 85% relative humidity (ISOS-D3). This work marks an important progress toward the realization of efficient and stable flexible perovskite photovoltaics for commercialization.
CRIS-Team Scopus Importer:2024-08-16

Fully Printed Infrared Photodetectors from PbS Nanocrystals with Perovskite Ligands - Yousefiamin, Amirabbas; Killilea, Niall Andrew; Sytnyk, Mykhailo; Maisch, Philipp; Tam, Kwok-Kan; Egelhaaf, Hans-Joachim; Langner, Stefan; Stubhan, Tobias; Brabec, Christoph; Rejek, Tobias; Halik, Marcus; Poulsen, Katharina; et al. (ACS nano, 2019)
Colloidal nanocrystals from PbS are successfully applied in highly sensitive infrared photodetectors with various device architectures. Here, we demonstrate all-printed devices with high detectivity (similar to 10(12) cm Hz(1/2) /W) and a cut-off frequency of >3 kHz. The low material consumption (<0.3 mg per detector) and short processing time (14 s per detector) enabled by the automated printing promises extremely low device costs. To enable all-printed devices, an ink formulation was developed based on nanocrystals stabilized by perovskite-like methylammonium iodobismuthate ligands, which are dispersed in a ternary solvent. Fully inkjet printed devices based on this solvent were achieved with printed silver electrodes and a ZnO interlayer. Considerable improvements were obtained by the addition of small amounts of the polymer poly(vinylpyrrolidone) to the ink. The polymer improved the colloidal stability of the ink and its film-formation properties and thus enabled the scalable printing of single detectors and detector arrays. While photoconductors were shown here, the developed ink will certainly find application in a series of further electronic devices based on nanocrystals from a broad range of materials.
Keywords: colloidal nanocrystals; infrared detectors; inkjet printing; PbS; solution processing

Fully printed organic solar modules with bottom and top silver nanowire electrodes - Tam, Kai Cheong; Kubis, Peter; Maisch, Philipp; Brabec, Christoph; Egelhaaf, Hans-Joachim (Progress in Photovoltaics, 2021)
One of the advantages of organic photovoltaics (OPV) over other contemporary technologies is its relative ease of processing. There are, however, very few works that have realized fully printed devices, including the bottom electrode, let alone with a scalable process in a reasonable device size (>1 cm(2)). In this work, design steps and optimization processes towards fully printed OPV modules with scalable processes are demonstrated for the first time. An overview on issues related to upscaling with printed electrodes is first provided. The various issues are then addressed by a rational design process supported by measurements and calculations. Finally, a set of fully printed OPV modules are fabricated using these optimized parameters that have over 3.5-cm(2) active area with 5% efficiency. For the first time, this work has also demonstrated the process compatibility of fully printed device structures with non-fullerene acceptor systems, which enables more design opportunities for the current generation of high-performance OPV materials.
CRIS-Team WoS Importer:2021-12-31

Fully printed organic tandem solar cells using solution-processed silver nanowires and opaque silver as charge collecting electrodes - Guo, Fei; Li, Ning; Radmilovic, Vuk V.; Radmilovic, Velimir R.; Turbiez, Mathieu; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (Energy and Environmental Science, 2015)
We report in this work efficient, fully printed tandem organic solar cells (OSCs) using solution-processed silver as the reflective bottom electrode and silver nanowires as the transparent top electrode. Employing two different band-gap photoactive materials with complementary absorption, the tandem OSCs are fully printed under ambient conditions without the use of indium tin oxide and vacuum-based deposition. The fully printed tandem devices achieve power conversion efficiencies of 5.81% (on glass) and 4.85% (on flexible substrate) without open circuit voltage (Voc) losses. These results represent an important progress towards the realization of low-cost tandem OSCs by demonstrating the possibility of printing efficient organic tandem devices under ambient conditions onto production relevant carrier substrates.

Fully solution-processed, light-weight, and ultraflexible organic solar cells - Güler, Ezgi; Distler, Andreas; Basu, Robin; Brabec, Christoph; Egelhaaf, Hans-Joachim (Flexible and Printed Electronics, 2022)
Organic photovoltaic (OPV) devices have the potential to be superior to other PV technologies for the use in applications that require very high flexibility or maximum specific power (power-per-weight ratio), such as textile integration, wearable electronics, or outer space applications. However, OPV devices also require encapsulation by barrier films to reduce the degradation driven by extrinsic factors, which in turn limits their flexibility and leads to lower specific power values. In this work, fully solution-processed (including both electrodes) semitransparent organic solar cells (OSCs) with performance comparable with conventional indium tin oxide-based devices are processed directly onto different barrier films of varying thicknesses. Direct cell fabrication onto barrier films leads to the elimination of the additional polyethylene terephthalate substrate and one of the two adhesive layers in the final stack of an encapsulated OPV device by replacing the industrial state-of-the-art sandwich encapsulation with a top-only encapsulation process, which yields significantly thinner and lighter 'product-relevant' PV devices. In addition to the increase of the specific power to 0.38 W g(-1), which is more than four times higher than sandwich-encapsulated devices, these novel OSCs exhibit better flexibility and survive 5000 bending cycles with 4.5 mm bending radius. Moreover, the devices show comparable stability as conventionally encapsulated devices under constant illumination (1 sun) in ambient air for 1000 h. Finally, degradation under damp heat conditions (65 degrees C, 85% rh) was investigated and found to be determined by a combination of different factors, namely (UV) light soaking, intrinsic barrier properties, and potential damaging of the barriers during (laser) processing.
CRIS-Team WoS Importer:2022-05-13
Keywords: solution-processability; specific power; organic photovoltaics; silver nanowire; transparent electrodes; flexible electronics; barrier films

Fully Solution Processed Pure α-Phase Formamidinium Lead Iodide Perovskite Solar Cells for Scalable Production in Ambient Condition - Yang, Fu; Dong, Lirong; Jang, Dongju; Tam, Kai Cheong; Zhang, Kaicheng; Li, Ning; Guo, Fei; Li, Cong; Arrive, Charline; Bertrand, Mélanie; Brabec, Christoph; Egelhaaf, Hans-Joachim (Advanced Energy Materials, 2020)
Manufacturing commercially viable perovskite solar cells still requires appropriate low-temperature and scalable deposition processes to be developed. While α-phase FAPbI3 has higher thermal stability and broader absorption than MAPbI3, there still is no report of a pure α-phase FAPbI3 perovskite film obtained by a scalable printing method. Moreover, spontaneous conversion of the α-phase to non-perovskite δ-phase under ambient conditions poses a serious challenge for practical applications. Herein, a scalable and fully solution based printing method for the fabrication of pure α-phase FAPbI3 perovskite solar cells is reported. Through adding N-methyl pyrrolidone and methylammonium chloride to the dimethylformamide based precursor solution to control the crystallization, and vacuum or air-flow assisted film drying, pure α-FAPbI3 phase is obtained by doctor blading. The resulting α-FAPbI3 film is highly stable, with no δ-FAPbI3 phase being formed even after keeping it in an ambient atmosphere over a period of 200 days without encapsulation. In addition, a fully solution processed PSC with a PCE of 16.1% is processed by the vacuum assisted method, and 17.8% by the air-flow assisted method. Replacing silver with a printed carbon electrode provides a stable PCE up to 15% for the vacuum assisted and 16.4% for the air-flow assisted method, which is the highest performance of FAPbI3 solar cells to date. Compared with MAPbI3, the fully printed FAPbI3 perovskite devices exhibit a remarkable thermal stability in humid atmospheres which makes them a promising candidate for scalable production and commercialization.
CRIS-Team Scopus Importer:2020-10-02
Keywords: carbon electrodes; doctor blades; fully printed devices; long-term stability; α-FAPbI

Fully Solution-Processed Small Molecule Semitransparent Solar Cells: Optimization of Transparent Cathode Architecture and Four Absorbing Layers - Min, Jie; Bronnbauer, Carina; Zhang, Zhi-Guo; Cui, Chaohua; Luponosov, Yuriy N.; Ata, Ibrahim; Schweizer, Peter; Przybilla, Thomas; Guo, Fei; Ameri, Tayebeh; Forberich, Karen; Spiecker, Erdmann; et al. (Advanced Functional Materials, 2016)
Semitransparent solar cells (SSCs) can open photovoltaic applications in many commercial areas, such as power-generating windows and building integrated photovoltaics. This study successfully demonstrates solution-processed small molecule SSCs with a conventional configuration for the presently tested material systems, namely BDTT-S-TR:PCBM, N(Ph-2T-DCN-Et):PCBM, SMPV1:PCBM, and UU07:PCBM. The top transparent cathode coated through solution processes employs a highly transparent silver nanowire as electrode together with a combination interface bilayer of zinc oxide nanoparticles (ZnO) and a perylene diimide derivative (PDINO). This ZnO/PDINO bilayer not only serves as an effective cathode buffer layer but also acts as a protective film on top of the active layer. With this integrated contribution, this study achieves a power conversion efficiency (PCE) of 3.62% for fully solution-processed SSCs based on BDTT-S-TR system. Furthermore, the other three systems with various colors exhibited the PCEs close to 3% as expected from simulations, demonstrate the practicality and versatility of this printed semitransparent device architecture for small molecule systems. This work amplifies the potential of small molecule solar cells for window integration.
Keywords: building integrated photovoltaics; interface bilayer; power conversion efficiency; semitransparent solar cells; small molecule

Fully Solution-Processing Route toward Highly Transparent Polymer Solar Cells - Guo, Fei; Kubis, Peter; Stubhan, Tobias; Li, Ning; Baran, Derya; Przybilla, Thomas; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (ACS Applied Materials and Interfaces, 2014)
We report highly transparent polymer solar cells using metallic silver nanowires (AgNWs) as both the electron- and hole-collecting electrodes. The entire stack of the devices is processed from solution using a doctor blading technique. A thin layer of zinc oxide nanoparticles is introduced between photoactive layer and top AgNW electrode which plays decisive roles in device functionality: it serves as a mechanical foundation which allows the solution-deposition of top AgNWs, and more importantly it facilitates charge carriers extraction due to the better energy level alignment and the formation of ohmic contacts between the active layer/ZnO and ZnO/AgNWs. The resulting semitransparent polymer:fullerene solar cells showed a power conversion efficiency of 2.9%, which is 72% of the efficiency of an opaque reference device. Moreover, an average transmittance of 41% in the wavelength range of 400-800 nm is achieved, which is of particular interest for applications in transparent architectures.
Keywords: semitransparent polymer solar cells; fully solution processing; OPV; ITO-free

Fundamental study of the temperature ramp-up influence for 3C-SiC hetero-epitaxy on silicon (100) - Hens, Philip; Wagner, G.; Hölzing, A.; Hock, R.; Wellmann, Peter (Materials Science Forum, 2010)
Usually a waiting step at around 1000 degrees C to 1100 degrees C during the carbonization step for 3C-SiC on silicon is implemented for establishing a closed carbon layer to prevent the formation of voids. The latter, however, may lead to non-ideal nucleation conditions for high quality layers with a low density of domain boundaries. Our investigations indicate that a continuous ramp-up as fast as possible with no waiting step would be preferable. The worst layer quality, as measured by peak intensity and FWHM of the (200) reflection of 3C-SiC, can be found at a temperature of about 1000 degrees C, which indicates that here the nucleation rate would be the highest. So longer periods within this temperature range should be avoided by applying high ramping speeds during the carbonization ste
Keywords: Carbonization; Heteroepitaxy; X-Ray Diffraction (XRD)

Gaining further insight into the effects of thermal annealing and solvent vapor annealing on time morphological development and degradation in small molecule solar cells - Min, Jie; Güldal, Nusret Sena; Guo, Jie; Fang, Chao; Jiao, Xuechen; Hu, Huawei; Heumüller, Thomas; Ade, Harald; Brabec, Christoph (Journal of Materials Chemistry A, 2017)
Numerous articles on thermal annealing (TA) and solvent vapor annealing (SVA) treatments have shown that both strategies effectively improve bulk morphology, reduce carrier recombination and thus improve photovoltaic performance of bulk heterojunction (BHJ) organic solar cells (OSCs). In previous work, we found that both TA and SVA treated devices based on a blend composed of a 3-ethyl-2-thioxothiazolidin-4-one containing molecule as donor (named DRCN5T) and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as acceptor show the similar photovoltaic performance, but their bulk microstructures are difference. Here employing in situ photoluminescence (PL) setup and X-ray scattering technologies, we found that the early stages of SVA remarkably affect the surface of film, and in contrast TA affects the whole bulk. Meanwhile, a plurality of experimental results all further confirm the different thermodynamics and kinetics of morphology evolution processed either by TA treatment or SVA treatment. Importantly, it was found that the SVA-treated film showed the increased photo-degradation in devices as compared to the TA-treated layer, resulting from obvious bulk morphology changes under illumination over 500 hours. The aim is to provide comprehensive insight into the influence of TA and SVA on time morphological evolution and degradation in OSCs. © 2017 The Royal Society of Chemistry.
Keywords: Annealing Butyric acid Heterojunctions Molecules Morphology Organic solar cells Solar power generation Thermodynamics X ray scattering

Galvanic Exchange in Colloidal Metal/Metal-Oxide Core/Shell Nanocrystals - Kriegner, Dominik; Sytnyk, Mykhailo; Groiss, Heiko; Yarema, Maksym; Grafeneder, Wolfgang; Walter, Peter; Dippel, Ann-Christin; Meffert, Matthias; Gerthsen, Dagmar; Stangl, Julian; Heiß, Wolfgang; Heiß, Wolfgang (Journal of Physical Chemistry C, 2016)
While galvanic exchange is commonly applied to metallic nanoparticles, recently its applicability was expanded to metal-oxides. Here the galvanic exchange is studied in metal/metal-oxide core/shell nanocrystals. In particular Sn/SnO is treated by Ag, Pt, Pt, and Pd. The conversion dynamics is monitored by in situ synchrotron X-ray diffraction. The Ag treatment converts the Sn cores to the intermetallic AgSn (x ∼ 4) phase, by changing the core's crystal structure. For the analogous treatment by Pt, Pt, and Pd, such a galvanic exchange is not observed. This different behavior is caused by the semipermeability of the naturally formed SnO shell, which allows diffusion of Ag but protects the nanocrystal cores from oxidation by Pt and Pd ions.
Keywords: Crystal structure; Metal nanoparticles; Metallic compounds; Metals; Nanocrystals; Palladium; Platinum; Tin; X ray diffraction Colloidal metals; Core/shell nanocrystals; Galvanic exchange; In-situ synchrotrons; Metal oxides; Metallic nanoparticles; Semipermeability

(Gd,Lu)AlO3:Dy3+ and (Gd,Lu)(3)Al5O12:Dy3+ as high-temperature thermographic phosphors - Hertle, Ellen Elisabeth; Chepyga, Liudmyla; Osvet, Andres; Brabec, Christoph; Batentschuk, Miroslaw; Will, Stefan; Zigan, Lars (Measurement Science & Technology, 2019)
A comparative investigation of the thermographic properties of Dy3+-doped gadolinium aluminum perovskite GdAlO3 (GAP) and gadolinium aluminum garnet Gd3Al5O12 (GAG) was performed with special regard to the suitability of these materials for surface thermometry in harsh measurement environments. The phosphors were synthesized by conventional high-temperature solid-state method using lithium fluoride (LiF) as a flux. The effects of substituting Gd3+ by Lu3+ ions on the stability of the garnet structure and the luminescence properties of the phosphors were investigated. An efficient energy transfer from Gd3+ to Dy3+ resulted in significantly stronger Dy3+ emission obtained through Gd3+ excitation at 275 nm compared to direct excitation of Dy3+ at 352 nm. The luminescence intensity of GAP:Dy3+ with Lu3+ substitution was three times higher at room temperature compared to GAP:Dy3+. Due to this intensity enhancement, the range of temperature measurements by the intensity ratio and decay time methods was extended from 900 K to 1100 K. The luminescence intensity of (Gd,Lu)AG:Dy3+ was doubled at room temperature compared to (Gd,Lu)AP:Dy3+ and the limit for reliable temperature measurements by the above mentioned methods was increased up to 1600 K.
CRIS-Team WoS Importer:2019-02-21
Keywords: phosphor thermometry; GAP; GAG; laser diagnostics; high temperature

General Observation of Photocatalytic Oxygen Reduction to Hydrogen Peroxide by Organic Semiconductor Thin Films and Colloidal Crystals - Gryszel, Maciej; Sytnyk, Mykhailo; Jakesova, Marie; Romanazzi, Giuseppe; Gabrielsson, Roger; Heiß, Wolfgang; Glowacki, Eric Daniel (ACS Applied Materials and Interfaces, 2018)
Low-cost semiconductor photocatalysts offer unique possibilities for industrial chemical transformations and energy conversion applications. We report that a range of organic semiconductors are capable of efficient photocatalytic oxygen reduction to H2O2 in aqueous conditions. These semiconductors, in the form of thin films, support a 2-electron/2-proton redox cycle involving photoreduction of dissolved O2 to H2O2, with the concurrent photooxidation of organic substrates: formate, oxalate, and phenol. Photochemical oxygen reduction is observed in a pH range from 2 to 12. In cases where valence band energy of the semiconductor is energetically high, autoxidation competes with oxidation of the donors, and thus turnover numbers are low. Materials with deeper valence band energies afford higher stability and also oxidation of H2O to O2. We found increased H2O2 evolution rate for surfactant-stabilized nanoparticles versus planar thin films. These results evidence that photochemical O2 reduction may be a widespread feature of organic semiconductors, and open potential avenues for organic semiconductors for catalytic applications. © 2018 American Chemical Societ
Keywords: photocatalysis; photochemistry; oxygen reduction reaction; photoanodes; organic semiconductors; hydrogen peroxide

Generation of void-like structures during hot-hydrogen etching of Si substrates for 3C-SiC epitaxy - Hens, Philip; Mueller, J.; Fahlbusch, Lars; Spiecker, E.; Wellmann, Peter; Spiecker, Erdmann (Materials Science Forum, 2011)
A new type of void-like structure has been identified in thin 3C-SiC heteroepitaxial layers grown on silicon substrates. Similar surface structures can be found in micrographs published in the literature but have not been addressed so far. We propose a mechanism which explains the formation of these "type II voids" as result of hot-hydrogen etching. Type II voids seem to act as nucleation sites for the well-known faceted voids formed beneath the 3C-SiC layer during seeding (type I voids). Suppression of type II voids by appropriate high temperature cleaning steps therefore reduces the overall density of detrimental type I void
Keywords: Silicon Carbide; 3C-SiC; Heteroepitaxy; Crystal growth; Voids

Georeferencing of photovoltaic modules from aerial infrared videos using structure-from-motion - Bommes, Lukas; Buerhop-Lutz, Claudia; Pickel, Tobias; Hauch, Jens; Brabec, Christoph; Peters, Ian Marius (Progress in Photovoltaics, 2022)
To identify abnormal photovoltaic (PV) modules in large-scale PV plants economically, drone-mounted infrared (IR) cameras and automated video processing algorithms are frequently used. While most related works focus on the detection of abnormal modules, little has been done to automatically localize those modules within the plant. In this work, we use incremental structure-from-motion to automatically obtain geocoordinates of all PV modules in a plant based on visual cues and the measured GPS trajectory of the drone. In addition, we extract multiple IR images of each PV module. Using our method, we successfully map 99.3% of the 35,084 modules in four large-scale and one rooftop plant and extract over 2.2 million module images. As compared to our previous work, extraction misses 18 times less modules (one in 140 modules as compared to one in eight). Furthermore, two or three plant rows can be processed simultaneously, increasing module throughput and reducing flight duration by a factor of 2.1 and 3.7, respectively. Comparison with an accurate orthophoto of one of the large-scale plants yields a root mean square error of the estimated module geocoordinates of 5.87 m and a relative error within each plant row of 0.22 m to 0.82 m. Finally, we use the module geocoordinates and extracted IR images to visualize distributions of module temperatures and anomaly predictions of a deep learning classifier on a map. While the temperature distribution helps to identify disconnected strings, we also find that its detection accuracy for module anomalies reaches, or even exceeds, that of a deep learning classifier for seven out of ten common anomaly types. The software is published at https://github.com/LukasBommes/PV-Hawk.
CRIS-Team Scopus Importer:2022-04-29
Keywords: deep learning; defect detection; drone; georeferencing; mapping; PV plant inspection; structure-from-motion; thermography

Germanium Incorporation during PVT Bulk Growth of Silicon Carbide - Hens, Philip; Künecke, Ulrike; Konias, Katja; Hock, Rainer; Wellmann, Peter (Materials Science Forum, 2009)
Silicon carbide as a material for electronic devices still has Substantial problems concerning its structural quality and defects. It has been shown that dopants call have a big influence on structural properties like poly-type stability and dislocation statistics [1]. We will discuss the effect of an isoelectronic dopant in silicon carbide. Germanium, being a member of the 4(th) group in the periodic table of elements like silicon and carbon, will not influence the electrical properties of the material such as e.g. aluminum. In Our experiments we reached concentrations of up to 1*10(20) cm(-3). We have observed all impact on the polytype stability during sublimation growth with in-situ germanium incorporation. We investigated all influence on the dislocation statistics during growth and, hence, varying germanium concentration. We found only a slight decrease in mobility during Hall measurements but no severe changes in electrical properties of the materia
Keywords: Bulk Growth; Dislocation; EDX; Germanium; Hall; Lattice Parameter

Giant magnetoresistance effect in a new hybrid granular ferromagnet semiconductor system - MnAs nanomagnets imbedded in LT-GaAs - Wellmann, Peter; Garcia, J.M.; Feng, J.-L; Petroff, P.M. (The physics of semiconductors – World Scientific, proceedings of ICPS24th conference (1999), 1999)

Giant magnetoresistance in a low-temperature GaAs/MnAs nanoscale ferromagnet hybrid structure - Wellmann, Peter; Garcia, J.M.; Feng, J.-L; Petroff, P.M. (Applied Physics Letters, 1998)
We report the observation of a giant magnetoresistance effect in a low-temperature LT-!GaAs/MnAs nanoscale ferromagnet hybrid structure. The MnAs nanomagnets are formed by ion implantation of Mn into LT GaAs and subsequent annealing. We have studied the magnetotransport using a vertically biased p1-GaAs/LT-GaAs:MnAs/p1-GaAs structure. A negative magnetoresistance (Dr /r5@r (B)2r (0)#/r(0)) of up to 280% (B57 T) is observed at low temperatures (T,20 K), which changes its sign from negative to positive between T=15 K and T=20 K. The value of the positive magnetoresistance decreases with increasing temperature from 115% (20 K) to 1.4% (300 K). The magnetoresistance variations with B and T are correlated with the nanomagnet spacing in the structure.<br

Giant magnetoresistance in a low-temperature grown GaAs with imbedded MnAs nanomagnets - Wellmann, Peter; Garcia, J.M.; Feng, J.-L; Petroff, P.M. (Physics of Microstructured Semiconductors, Vol.6, 1998)

Giant Rashba Splitting in CH3NH3PbBr3 Organic-Inorganic Perovskite - Niesner, Daniel; Wilhelm, Max; Levchuk, Ievgen; Osvet, Andres; Shrestha, Shreetu; Batentschuk, Miroslaw; Brabec, Christoph; Fauster, Thomas (Physical Review Letters, 2016)
As they combine decent mobilities with extremely long carrier lifetimes, organic-inorganic perovskites open a whole new field in optoelectronics. Measurements of their underlying electronic structure, however, are still lacking. Using angle-resolved photoelectron spectroscopy, we measure the valence band dispersion of single-crystal CH3NH3PbBr3. The dispersion of the highest energy band is extracted applying a modified leading edge method, which accounts for the particular density of states of organic-inorganic perovskites. The surface Brillouin zone is consistent with bulk-terminated surfaces both in the low-temperature orthorhombic and the high-temperature cubic phase. In the low-temperature phase, we find a ring-shaped valence band maximum with a radius of 0.043 Å-1, centered around a 0.16 eV deep local minimum in the dispersion of the valence band at the high-symmetry point. Intense circular dichroism is observed. This dispersion is the result of strong spin-orbit coupling. Spin-orbit coupling is also present in the room-temperature phase. The coupling strength is one of the largest ones reported so far.

Global numerical simulation of heat and mass transfer during SiC bulk crystal PVT growth - Selder, Markus; Kadinski, Lev; Durst, Franz; Straubinger, Thomas; Hofmann, Heinz-Dieter; Wellmann, Peter (Materials Science Forum, 2000)
Modeling results of a global heat and mass transfer analysis of the SIC bulk growth process in an inductively heated PVT reactor are presented. The modeling approach is summarized and its reliability is shown by comparing experimental data to simulation results. The temporal evolution of the temperature gradients at the crystal surface during the growth process is analyzed and related to the radial growth rate distribution. The species fluxes at the surface of the source are investigate
Keywords: Global Heat Transfer; Mass Transfer; Numerical Modeling; Physical Vapor Transport; SiC Bulk Growth

Global numerical simulation of heat and mass transfer for SiC bulk crystal growth by PVT - Selder, Markus; Kadinski, Lev; Makarov, Y.; Durst, Franz; Wellmann, Peter; Straubinger, Thomas; Hofmann, Heinz-Dieter; Karpov, S.; Ramm, M. (Journal of Crystal Growth, 2000)
A modeling approach for the numerical simulation of heat and mass transfer during SiC sublimation growth in inductively heated physical vapor transport (PVT) reactors is introduced. The physical model is based on the two-dimensional solution of the coupled differential equations describing mass conservation, momentum conservation, conjugate heat transfer including surface to surface radiation, multicomponent chemical species mass transfer and advective flow. The model also includes the Joule volume heat sources induced by the electromagnetic field. The evolution of the temperature profiles inside the crucible and of the crystallization front is studied. The radial temperature gradient at the crystal/gas interface causes strong radial non-uniformity of the growth rate and, in turn, influences the shape of the growing crystal. Results of calculations are compared to experimental observations to analyse the validity of the modeling approach. Both the computed growth rates, their temporal evolution and the shape of the growing crystal agree with experimental dat
UnivIS-Import:2015-10-26:Pub.2000.tech.ITC.stmmec.global
Keywords: SiC bulk growth; Physical vapor transport; Numerical modeling; Global heat and mass transfer

Graded 2D/3D Perovskite Heterostructure for Efficient and Operationally Stable MA-Free Perovskite Solar Cells - Yao, Qin; Xue, Qifan; Li, Zhenchao; Zhang, Kaicheng; Zhang, Teng; Li, Ning; Yang, Shihe; Brabec, Christoph; Yip, Hin-Lap; Cao, Yong (Advanced Materials, 2020)
Almost all highly efficient perovskite solar cells (PVSCs) with power conversion efficiencies (PCEs) of greater than 22% currently contain the thermally unstable methylammonium (MA) molecule. MA-free perovskites are an intrinsically more stable optoelectronic material for use in solar cells but compromise the performance of PVSCs with relatively large energy loss. Here, the open-circuit voltage (V-oc) deficit is circumvented by the incorporation of beta-guanidinopropionic acid (beta-GUA) molecules into an MA-free bulk perovskite, which facilitates the formation of quasi-2D structure with face-on orientation. The 2D/3D hybrid perovskites embed at the grain boundaries of the 3D bulk perovskites and are distributed through half the thickness of the film, which effectively passivates defects and minimizes energy loss of the PVSCs through reduced charge recombination rates and enhanced charge extraction efficiencies. A PCE of 22.2% (certified efficiency of 21.5%) is achieved and the operational stability of the MA-free PVSCs is improved.
CRIS-Team WoS Importer:2020-06-05

Grain structure of thin-film silicon by zone melting recrystallization on SiC base layer - Kunz, T.; Hessmann, M. T.; Auer, R.; Bochmann, A.; Christiansen, S.; Brabec, Christoph (Journal of Crystal Growth, 2012)
The grain structure of thin-film silicon layers obtained by chemical vapor deposition and zone melting recrystallization (ZMR) on SiC barrier layers, as developed for thin-film solar cells, have been investigated by electron backscatter diffraction (EBSD). The occurrence of subgrain boundaries was checked by defect etching. Twin boundaries form 1 to 100 μm wide stripes, which are nearly parallel to the scan direction of ZMR. We find that stripe structure and the dominant grain orientations differ significantly from previously published ZMR layers grown on SiO surface. In a comprehensive model it is shown how the twinning structure and the dominant grain orientation can be related to the growth kinetics. The electronic activity of the defects was measured by electron beam induced current (EBiC). Contrary to other defects, the twin boundaries show no enhanced recombination. Therefore the found growth regime has potential advantages with respect of electronic properties of the layers. © 2012 Elsevier B.V. All rights reserved.
Keywords: A1. Defects; A1. Electron backscattering diffraction; A1. Twin boundaries; A3. Zone melting recrystallization; B1. Solar cells; B2. Semiconducting silicon

Granular Matter - special edition - Pöschel, Thorsten; Wolf, Dietrich (Granular Matter, 2012)

Graphene Oxide Thin Films: Synthesis and Optical Characterization - Prías Barragán, J. J.; Gross, K.; Darío Perea, José; Killilea, Niall Andrew; Heiß, Wolfgang; Brabec, Christoph; Calderón, H. Ariza; Prieto, Pedro (ChemistrySelect, 2020)
The oxidized derivative of graphene named Graphene oxide (GO) are attractive materials as optoelectronic devices due to their optical response in the mid-infrared wavelength spectral range; however, very large-scaled synthesis methods and optical characterization are required. Here, GO thin films are fabricated on quartz by implementing simple two-step pyrolysis processes by using renewable bamboo as source material. The effect of carbonization temperature (TCA) on the compositional, vibrational, and optoelectronic properties of the system are investigated. It was found that as TCA increases, graphite conversion rises, oxygen coverage reduces from 17 % to 4 %, and the band-gap energy monotonically decreases from 0.30 to 0.11 eV. Theoretical predictions of the energy band-gap variations with the oxide coverage obtained via density functional theory (DFT) computational simulations agree well with the experimental results, providing evidence of oxygen-mediated charge-transport scattering. Interestingly, in the optical response, increased TCA results in a blue-shift of the absorption and the absorbance spectrum can be correlated with the large size distribution of the graphitic nano-crystals of the samples. These results suggest that graphene oxide-bamboo pyroligneous acid (GO) thin films exhibit optoelectronic response useful in developing photodetectors and emitter devices in the mid-infrared (MIR) spectral range.
CRIS-Team Scopus Importer:2020-10-23
Keywords: band-gap energy; COSMO-RS; DFT computational simulations; graphene oxide; HR-TEM images; oxygen coverage; Photoluminescence; UV-Vis

"Green" synthesis of highly luminescent lead-free Cs2AgxNa1-xBiyIn1-yCl6 perovskites - Stroyuk, Oleksandr; Raievska, Oleksandra; Barabash, Anastasia; Batentschuk, Miroslaw; Osvet, Andres; Fiedler, Saskia; Resch-Genger, Ute; Hauch, Jens; Brabec, Christoph (Journal of Materials Chemistry C, 2022)
A new "green" and mild synthesis of highly stable microcrystalline Cs2AgxNa1-xBiyIn1-yCl6 (CANBIC) perovskites under ambient conditions was developed that is scalable to the multi-gram production. Under UV illumination, the CANBIC perovskites emit intense broadband photoluminescence (PL) with a quantum yield (QY) of 92% observed for x = 0.35 and y = 0.01-0.02. The combination of strong UV absorbance and broadband visible emission, high PL QY, and long PL lifetimes of up to 1.4 mu s, along with an outstanding stability makes these CANBICs a promising material class for many optical applications.
CRIS-Team WoS Importer:2022-06-24

Growing bulk-like 3C-SiC from seeding material produced by CVD - Schuh, Philipp; Arzig, Matthias; Litrico, G.; La Via, F.; Mauceri, M.; Wellmann, Peter (physica status solidi (a), 2017)
We present a process to transfer CVD grown heteroepitaxial 3C-SiC on Si onto polycrystalline SiC, involving an etching step to get rid of the Si and a homogeneous carbon glue deposit, facilitating the resulting compound to be used as a seeding material for further growth process. In a sublimation sandwich setup, realized within an inductively heated physical vapor transport reactor, used for bulk growth of SiC, the thickness of the 3C-SiC seed was increased up to 850μm while keeping the cubic polytype. With the introduction of Ta as a carbon getter, the gas phase composition is optimized in order to achieve an improved growth front. Single crystalline growth is confirmed by Laue diffraction and Raman measurements. The Raman peaks are shifted to higher wavenumbers, indicating compressive stress in the grown samples. Furthermore, a scale up of the process is demonstrated, showing the feasibility of growing 3C-SiC on an area of 10.5cm in a 2inch setup featuring a thickness of approximately 570μ
Keywords: 3C-SiC; bulk crystals; layer transfer; physical vapor transport

Growth and characterization of C-13 enriched 4H-SiC for fundamental materials studies - Jang, Yeon-Suk; Sakwe, Aloysius; Wellmann, Peter; Juillaguet, Sandrine; Peyre, Herve; Camassel, J.; Steeds, J. W. (Materials Science Forum, 2007)
We have carried out the growth and basic characterization of isotopically enriched 4H-(SiC)-C-13 crystals. in recent years the growth of 13 C enriched 6H-SiC has been performed in order to carry out fundamental materials studies (e.g. determination of phonon energies, fundamental bandgap shift, carbon interstitial defect study, analysis of the physical vapor transport (PVT) growth process). For electronic device applications, however, the 4H-SiC polytype is the favored material, because it offers greater electron mobility. In this paper we present the growth of 4H-(SiC)-C-13 single crystals with up to 60% of C-13 concentration. From a physical point of view we present first results on phonons as well as the fundamental bandgap energy shift due to 13C incorporation into the SiC lattice.
Keywords: (SiC)-C-13

Growth and luminescent properties of TbAlO3 - Zorenko, Yu.; Gorbenko, V.; Vozniak, T.; Batentschuk, Miroslaw; Osvet, Andres; Winnacker, Albrecht; et al. (physica status solidi (a), 2010)
The paper is dedicated to the investigation of growth processes by liquid phase epitaxy (LPE) and the luminescent properties of single-crystalline films (SCFs) of TbAlO_3 terbium-aluminum perovskite (TbAP) perovskite doped with manganese ions. We found that the Mn2+ and Mn3+ or even Mn5+ states can occur in TbAP:Mn SCF depending on the concentration of manganese ions in the 0.01–1.1 at.% range. The Mn2+ ions in TbAP host possess orange luminescence in the band peaked at 572 nm with a lifetime of 1.24 ms at 300 K that is caused by the ^4T1 i̊ghtarrow6 A1 radiative transitions. The cascade energy-transfer processes can be realized in TbAP:Mn SCF: (i) from 5d–4f states of Tb3+ cations to Mn2+ ions; (ii) from Mn2+ ions to 4f states of Tb3+ cations. The latest process strongly decreases the efficiency of Mn2+ luminescence in TbAlO_3 perovskite with respect to the Tb_3Al5O12 garnet host.
EAM Import::2019-03-13

Growth conditions and in situ computed tomography analysis of facetted bulk growth of SiC boules - Arzig, Matthias; Salamon, Michael; Uhlmann, Norman; Johansen, Bertil Andre; Wellmann, Peter (Materials Science Forum, 2018)
Two 3inch SiC boules were grown in a PVT setup using source material of different packing density. During the growth, in-situ computed tomography of the growing boules showed differences in the development of the growth interface. A slightly bent growth interface was found for the smaller packing density. For the higher packing density the resulting crystal exhibits the onset of 6 pyramidal facets on its flanks. Besides that, strong anisotropic lateral growth was found on its (000-1) facet. Numerical simulations show an impact of the powder on the thermal gradient in the growth cell and therefore on the supersaturation. It is discussed that a higher supersaturation can account for the anisotropy in the growth rate of the [1-100] and the [11-20] direction.<br
Keywords: Packing density; Supersaturation; Facet; In situ CT; Anisotropic lateral growth

Growth, defects and doping of 3C-SiC on hexagonal polytypes - Yakimova, Rositsa; Ivanov, Ivan G.; Vines, Lasse; Linnarsson, Margareta K.; Gällström, Andreas; Giannazzo, Filippo; Roccaforte, Fabrizio; Wellmann, Peter; Syväjärvi, Mikael; Jokubavicius, Valdas (ECS Journal of Solid State Science and Technology, 2017)
Technologies for the growth of 3C-SiC with crystalline quality and crystal size similar to hexagonal counterparts (6H- or 4H-SiC) are still at the laboratory stage. There are several challenges in the control of polytype stability and formation of structural defects which have to be eliminated to reveal the full potential of this material. Nevertheless, 3C-SiC has been explored for various energy, environment and biomedical applications which significantly benefit from the intrinsic semiconductor properties of this material. The future of 3C-SiC and its applications depends on the advances which will be made in improving crystalline quality, enlarging crystal size and controlling doping levels which have not been entirely explored due to the lack of high quality 3C-SiC substrates. This paper reviews recent progress in growth and doping of thick 3C-SiC layers on hexagonal SiC substrates using sublimation epitaxy. It covers the growth process on off-axis substrates and defects occurrence, as well as the issue of obtaining high resistivity materia
Keywords: 3C-SiC; co-doping; Sublimation epitaxy

Growth of large-area, stress-free, and bulk-like 3C-SiC (100) using 3C-SiC-on-Si in vapor phase growth - Schuh, Philipp; La Via, Francesco; Mauceri, Marco; Zielinski, Marcin; Wellmann, Peter (Materials, 2019)
We report on the reproducible growth of two inch 3C-SiC crystals using the transfer of chemical vapor deposition (CVD)-grown (100) oriented epitaxial layers. Additional experiments, in which the diameter of the free-standing layers is increased, are presented, indicating the upscale potential of this process. The nucleation and growth of cubic silicon carbide is supported by XRD and Raman measurements. The rocking curve data yield a full-width-at-half-maximum (FWHM) between 138 to 140 arc sec for such grown material. Analysis of the inbuilt stress of the bulk-like material shows no indications of any residual stress.
CRIS-Team Scopus Importer:2019-07-23
Keywords: 3C-SiC; Bulk; Large area; PVT; Stress-free; Sublimation sandwich

Growth of phosphorous-doped n-type 6H-SiC crystals using a modified PVT technique and phosphine as source - Desperrier, Patrick; Müller, Ralf; Winnacker, Albrecht; Wellmann, Peter (Materials Science Forum, 2004)
In this paper we report bulk SiC doping with phosphorous by the modified physical vapor transport (M-PVT) method using phosphine as source. Near infrared absorption mapping was carried out on longitudinal cuts of the SiC crystals in order to verify phosphorous doping. The phosphorous concentration determined by the way of glow discharge mass spectroscopy (GDMS) measurements was up to N-D = 1.8 (.) 10(17)cm(-3
Keywords: Doping; M-PVT; Phosphorous; Silicon Carbide (SiC)

Growth of SiC bulk crystals for application in power electronic devices - process design, 2D and 3D X-ray in situ visualization and advanced doping - Wellmann, Peter; Neubauer, Georg; Fahlbusch, Lars; Salamon, Michael; Uhlmann, Norman (Crystal Research and Technology, 2015)
Silicon carbide single crystals have become widely used as substrates for power electronic devices like diodes and electronic switches. Today, 4inch and 6inch wafer diameters are commercially available which are processed from vapor grown crystals. The state of the art physical vapor transport method may be called mature. Nevertheless, low defect density and uniform doping are still topics which can be further improved by current research and development of more sophisticated processes and process control. The aim of the paper is to review the physical vapor transport growth method as applied today. Special emphasis will be put on currently less advanced in situ growth monitoring tools based on 2D and 3D X-ray imaging that could be a tool for production monitoring. These techniques allow a precise determination of the crystal and source material evolution. Another topic will be the processing of highly conductive p-type 4H-SiC which is of particular interest for power electronic switches.
Keywords: SiC bulk growth; Physical Vapor Transport; In situ X-ray Visualization; Computer Tomography; Aluminum Doping

Growth of silicon carbide bulk crystals with a modified physical vapor transport technique - Müller, Ralf; Künecke, Ulrike; Queren, Desiree; Sakwe, Aloysius; Wellmann, Peter (Chemical Vapor Deposition, 2006)
In this paper, the development of the modified physical vapor transport (M-PVT) method for SiC bulk crystal growth is reviewed. For this technique, elements from CVD are combined with the conventional PVT (physical vapor transport) method to achieve a better process and particularly dopant control. To this end, an additional gas flow is introduced directly into the growth chamber of a PVT growth system. For stable crystal growth it is important that the additional gas flow is of the same order of magnitude as the SiC-species flow by sublimation. Doping experiments resulted in phosphorous concentrations up to 1.5 x 10(18) cm(-3) and aluminum concentrations up to 1.3 x 10(20) cm(-3) using a PH3-flow and a solid aluminum source in an external reservoir as dopant source, respectively. Also, the growth of a crystal with alternating p- and n-type regions for the investigation of the charge carrier-dependant dislocation evolution in SiC is presented to illustrate the outstanding flexibility that is offered by the M-PVT method.
Keywords: Dislocations; Doping; PVT method; SiC bulk growth

Growth rate control in SiC-physical vapor transport method through heat transfer modeling and non-stationary process conditions - Straubinger, Thomas; Bickermann, Matthias; Grau, M.; Hofmann, Heinz-Dieter; Kadinski, Lev; Müller, Georg; Selder, Markus; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2000)
The thermal data used were determined from pyrometrical measurements on the top and bottom of the crucible during the experiments and were combined with simulations of the 2-dimensional heat transfer in the assembly. The latter allowed us to obtain the temperatures (source, crystal) inside the reaction chamber which were not assessable by direct measurement
Keywords: Heat Transfer; Mass Transport; Non-Stationary Process

Guest editorial: Special section on organic photovoltaics - Brabec, Christoph; Brabec, Christoph J.; Lane, Paul; Kafafi, Zakya H. (Journal of Photonics for Energy, 2012)
Organic photovoltaics (OPVs) have a long history, stretching back three decades into the 1980s, when first studies were conducted on the photogeneration of charge carriers at interfaces in organic solids. Compared to inorganic photovoltaics, OPVs offer many advantages, such as low cost, high throughput production, flexible devices, lightweight products, as well as custom-designed colors. In the last decade, research activities have intensified to increase the power conversion efficiencies and lifetimes of OPVs and make them more competitive with their inorganic counterparts. Scientists and engineers worldwide have worked hard to exploit the inherent advantages of organic materials. A series of breakthroughs in materials, processing, and characterization have been reported in the last couple of years, leading to dramatic gains in the performance of organic solar cells. The most recent certified power conversion efficiencies meet or exceed the 10% level for a solution-processable single-junction device, positioning OPVs as the next-generation solar cells. Companies such as Merck, BASF, Sumitomo, and Plextronics have started to commercialize organic semiconducting materials, while companies such as Konarka Technologies, Heliatek, Solarmer, and Mitsubishi have begun commercialization of organic solar modules. Further development is necessary in order to achieve OPVs with higher efficiencies and better lifetimes. There are demands for stable and low-band-gap semiconductors with excellent charge-carrier-transport properties; concepts to control the microstructure in bulk heterojunction composites are essential; the development of efficient and environmentally stable interface materials has to take place; and, finally, strategies for a cost-efficient and long-time stable packaging processes need to be developed. In addition, further fundamental understanding of the photophysical processes, including the different interfaces in organic solar cells, is essential to minimize energetic losses and combat device degradation. For the final product release, light propagation and light management need to become integrated in organic solar modules. In this special section of the Journal of Photonics for Energy, papers that address the above issues and challenges are presented. These papers are based partially on talks and posters given at the conference on Organic Photovoltaics XII at the SPIE Optics + Photonics meeting held in San Diego in August 2011. We believe that the readers will find the results of the studies discussed in these manuscripts interesting, educational, and stimulating, and we welcome any constructive feedback with regard to this special section.

Guideline for Efficiency Enhancement in Semi-Transparent Thin-Film Organic Photovoltaics with Dielectric Mirrors - Bronnbauer, Carina; Gasparini, Nicola; Brabec, Christoph; Forberich, Karen (Advanced Optical Materials, 2016)
Semi-transparent organic solar cells (ST-OSCs) show a unique potential to be integrated in windows due to their outstanding characteristics such as high transparency and color-adjustability. In order to achieve both, high transparency and high efficiency, the use of dielectric mirrors is an excellent concept. However, such a mirror will not only improve the photocurrent generated by a solar cell but also cause losses in transparency. In this work, a theoretical model is developed that predicts the effect of the dielectric mirror on the balance between photocurrent enhancement and transparency loss depending on the spectral shape of the ST-OSC absorption. Experimental investigations with three fully printed ST-OSCs showing different absorption characteristics underline the validity of these studies. It is concluded that ST-OSCs with broad absorption spectra ranging from the short wavelength region over the visible to at least 950 nm are most suitable for the implementation of a dielectric mirror. A narrower absorption spectrum or a shift of the spectrum toward longer wavelengths makes an increase in photoactive layer thickness more beneficial than the attachment of a dielectric mirror. Moreover, the dielectric mirror approach is an excellent strategy to obtain high photocurrents for materials which cannot be processed at high active layer thicknesses.
Keywords: bragg mirrors; dielectric mirrors; organic photovoltaics; printing; semi-transparent

Guidelines for Closing the Efficiency Gap between Hero Solar Cells and Roll-To-Roll Printed Modules - Lucera, Luca; Kubis, Peter; Fecher, Frank W.; Bronnbauer, Carina; Turbiez, Mathieu; Forberich, Karen; Ameri, Tayebeh; Egelhaaf, Hans-Joachim; Brabec, Christoph (Energy Technology, 2015)
One of the biggest challenges for the commercialization of polymer-based and other printed photovoltaic (PV) technologies is to establish reliable up-scaling processes that minimize the efficiency losses occurring during the transition from record laboratory cells to roll-to-roll (R2R) printed PV modules. This article reviews the latest advances in reducing the efficiency gap between record solar cells and large-area organic PV modules. The major loss sources are identified for the most popular cell architectures and categorized into optical, electrical, and processing-related contributions. Their relative shares in the overall efficiency drop are quantified through optical and electrical simulations. Further potential sources of efficiency loss, such as the replacement of halogenated by green solvents for active layer processing, are also addressed. Finally, the effect of reduced efficiency gaps on the production costs of R2R printed modules is discussed, demonstrating that values as low as €0.5Wp -1 (the nominal power of a solar module/cell) can be achieved. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Photovoltaics; Polymers; Printing; Roll-to-roll processing; Solar cells

High Al-doping of SiC using a modified PVT (M-PVT) growth set-up - Müller, Ralf; Künecke, Ulrike; Weingärtner, Roland; Schmitt, Holger; Desperrier, Patrick; Wellmann, Peter (Materials Science Forum, 2005)
Several highly aluminum doped SiC bulk crystals were grown with a modified PVT (M-PVT) method. To facilitate 4H-SiC formation, growth was conducted on the C-face. The samples were investigated using Hall measurements in the Van-der-Pauw geometry. Lowest room temperature values for specific resistivities were 0.09 &UOmega; cm for 6H-SiC and 0.2 &UOmega; cm for 4H-SiC, which are to our knowledge the lowest values yet reported in literature. Thus, resistivity values of < 0.2 &UOmega; cm, which are required for substrates in high power device applications, could be demonstrated for 4H-SiC. Remarkably, in very highly doped samples the type of conduction could not be determined by Hall measurement
Keywords: Al-Doping; p-Type; 4H-SiC; 6H-SiC; SiC Bulk Growth; PVT Method; Hall Effect

High-efficiency and air-stable P3HT-based polymer solar cells with a new non-fullerene acceptor - Holliday, Sarah; Ashraf, Raja Shahid; Wadsworth, Andrew; Baran, Derya; Yousaf, Syeda Amber; Nielsen, Christian B.; Tan, Ching-Hong; Dimitrov, Stoichko D.; Shang, Zhengrong; Gasparini, Nicola; Alamoudi, Maha; Laquai, Frederic; et al. (Nature Communications, 2016)
Solution-processed organic photovoltaics (OPV) offer the attractive prospect of low-cost, light-weight and environmentally benign solar energy production. The highest efficiency OPV at present use low-bandgap donor polymers, many of which suffer from problems with stability and synthetic scalability. They also rely on fullerene-based acceptors, which themselves have issues with cost, stability and limited spectral absorption. Here we present a new non-fullerene acceptor that has been specifically designed to give improved performance alongside the wide bandgap donor poly(3-hexylthiophene), a polymer with significantly better prospects for commercial OPV due to its relative scalability and stability. Thanks to the well-matched optoelectronic and morphological properties of these materials, efficiencies of 6.4% are achieved which is the highest reported for fullerene-free P3HT devices. In addition, dramatically improved air stability is demonstrated relative to other high-efficiency OPV, showing the excellent potential of this new material combination for future technological applications.

High efficiency and stability small molecule solar cells developed by bulk microstructure fine-tuning - Min, Jie; Jiao, Xuechen; Sgobba, Vito; Kan, Bin; Heumüller, Thomas; Rechberger, Stefanie; Spiecker, Erdmann; Guldi, Dirk Michael; Wan, Xiangjian; Chen, Yongsheng; Ade, Harald; Brabec, Christoph (Nano Energy, 2016)
Morphological control over the bulk heterojunction (BHJ) microstructure of a high-efficiency small molecule photovoltaic system composed of a quinquethiophene based molecule (DRCN5T) as electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as electron acceptor is demonstrated using three different post-processing strategies, including thermal annealing (TA), solvent vapor annealing (SVA), and two-step annealing (TA-SVA) treatments. We systematically analyze the processing condition-microstructure-device property relationships, explore the corresponding morphology evolution and their effects on carrier transport and recombination dynamics in BI-Js as well as understand the nature of phase-separation process resulting in light-induced degradation mechanisms. Within the investigated results, the causative relations between annealing sequence, photovoltaic parameters, morphology evolution and charge carrier dynamics are for the first time delineated. In addition, the observed trade-offs in device efficiency and stability with respect to the well-defined morphologies are highlighted. The in-depth picture of the bulk microstructure formation and its kinetic evolution as a function of the specific post-processing approaches is a valuable asset for the design of new photovoltaic materials and thin film nanoscale architectures that are more efficient and better aid future commercialization efforts. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords: Blend microstructure; Morphological control; Annealing sequence; Phase-separation; Charge carrier dynamics; Degradation mechanisms

High fill factor polymer solar cells comprising a transparent, low temperature solution processed doped metal oxide/metal nanowire composite electrode - Stubhan, Tobias; Krantz, Johannes; Li, Ning; Guo, Fei; Litzov, Ivan; Steidl, Matthias; Richter, Moses; Matt, Gebhard; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2012)
In this paper we report on the replacement for the commonly used ITO electrode material by a low temperature solution processed silver nanowire/(doped) metal oxide composite. Devices employing silver nanowires (AgNWs)/buffer layer electrodes with a photoactive layer of poly(3- hexylthiophene) (P3HT) and [6,6]-phenyl-C butyric acid methyl ester (PCBM) are showing a comparable performance to the ITO reference cell with fill factors (FF) of over 62% and a power conversion efficiency of ∼2.7%. Zinc oxide (ZnO) and highly conductive Al doped ZnO (AZO) are used as buffer layer. AgNW devices without a buffer layer have a high open circuit voltage (V ) but the FF and the short circuit current density (j ) are substantially lower. Overall it is demonstrated that AgNWs and the low temperature solution process of the buffer layer are an attractive device concept towards an indium free organic solar cell. © 2012 Elsevier B.V. All rights reserved.
Keywords: Aluminum-doped zinc oxide; Metal nanowires; Organic solar cells; Solution processed; Transparent electrode; Zinc oxide

High fill factor polymer solar cells incorporating a low temperature solution processed WO3 hole extraction layer - Stubhan, Tobias; Li, Ning; Luechinger, Norman A.; Halim, Samuel C.; Matt, Gebhard; Brabec, Christoph (Advanced Energy Materials, 2012)
We demonstrate solution-processed tungsten trioxide (WO) incorporated as hole extraction layer (HEL) in polymer solar cells (PSCs) with active layers comprising either poly(3-hexylthiophene) (P3HT) or poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2, 6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,50-diyl] (Si-PCPDTBT) mixed with a fullerene derivative. The WO layers are deposited from an alcohol-based, surfactant-free nanoparticle solution. A short, low-temperature (80 °C) annealing is sufficient to result in fully functional films without the need for an oxygen-plasma treatment. This allows the application of the WO buffer layer in normal as well as inverted architecture solar cells. Normal architecture devices based on WO HELs show comparable performance to the PEDOTPSS reference devices with slightly better fill factors and open circuit voltages. Very high shunt resistances (over 1 MO cm) and excellent diode rectification underline the charge selectivity of the solution-processed WO layers. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA.
Keywords: 1; 3-benzothiadiazole; Active Layer; Fill factor; Fullerene derivative; Functional films; High fills; Low temperature solutions; Low temperatures; Nanoparticle solutions; Oxygen-plasma treatment; PEDOT-PSS; Poly-3-hexylthiophene; Polymer Solar Cells; Reference devices; Shunt resistances; Solution-processed; Surfactant-free; Tungsten trioxide Engineering controlled terms: Open circuit voltage; Plasma applications; Solar cells; Tungsten Engineering main heading: Temperature

High Infrared Photoconductivity in Films of Arsenic-Sulfide-Encapsulated Lead-Sulfide Nanocrystals - Yakunin, Sergii; Dirin, Dmitry N.; Protesescu, Loredana; Sytnyk, Mykhailo; Tollabimazraehno, Sajjad; Humer, Markus; Hackl, Florian; Fromherz, Thomas; Bodnarchuk, Maryna I.; Kovalenko, Maksym V.; Heiß, Wolfgang (Acs Nano, 2014)
Highly photoconductive thin films of inorganic-capped PbS nanocrystal quantum dots (QDs) are reported. Stable colloidal dispersions of (NH4)(3)AsS3-capped PbS QDs were processed by a conventional dip-coating technique into a thin homogeneous film of electronically coupled PbS QDs. Upon drying at 130 degrees C, (NH4)(3)AsS3 capping ligands were converted into a thin layer of As2S3, acting as an infrared-transparent semiconducting glue. Photodetectors obtained by depositing such films onto glass substrates with interdigitate electrode structures feature extremely high light responsivity and detectivity with values of more than 200 A/W and 1.2 x 10(13) Jones, respectively, at infrared wavelengths up to 1400 nm. Importantly, these devices were fabricated and tested under ambient atmosphere. Using a set of time-resolved optoelectronic experiments, the important role played by the carrier trap states, presumably localized on the arsenic-sulfide surface coating, has been elucidated. Foremost, these traps enable a very high photoconductive gain of at least 200. The trap state density as a function of energy has been plotted from the frequency dependence of the photoinduced absorption (PIA), whereas the distribution of lifetimes of these traps was recovered from PIA and photoconductivity (PC) phase spectra. These trap states also have an important impact on carrier dynamics, which led us to propose a kinetic model for trap state filling that consistently describes the experimental photoconductivity transients at various intensities of excitation light. This model also provides realistic values for the photoconductive gain and thus may serve as a useful tool to describe photoconductivity in nanocrystal-based solids.
Keywords: lead sulfide; nanocrystals; inorganic ligands; photodetectors; trap states

Highly Efficient Bilayer Polymer Solar Cells Using the Method of Sequential Processing with Additive Bilayer - Lee, Jihoon; Jang, Soyeong; Tamilavan, Vellaiappillai; Li, Ning; Wang, Rong; Lüer, Larry; Lee, Dalyong; Yoon, Jung Won; Lee, Bo Ram; Choi, Hyosung; Park, Sung Heum; Brabec, Christoph (Solar RRL, 2023)
Despite the research value of bilayer organic solar cells (OSCs) for commercialization in the future, the bulk-heterojunction (BHJ) structure dominates the fabrication of OSCs because of its higher power conversion efficiency (PCE) compared with bilayer OSCs. Herein, four different types of bilayer OSC structures using sequential processing (SP) with an additive bilayer are investigated and considerably enhanced device performance is demonstrated. The performance of our bilayer devices based on a wide bandgap (PBDT-DPPD-TPD; P2) polymer and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) is improved from 2.88% for the conventional bilayer structure to 6.62%. More importantly, remarkable PCEs of 8.78% and 15.16% for PTB7-Th/PCBM and PM6/Y6 bilayer OSCs, respectively, using the SP with additive bilayer method are achieved and the inhomogeneity issues of the BHJ structure are successfully addressed. Herein, a novel way to overcome the low efficiency of bilayer OSCs is suggested and an unprecedented possibility of renovation, breaking the standardization of OSC research, is presented.
CRIS-Team Scopus Importer:2023-01-20
Keywords: bilayer structures; high efficiency; organic solar modules; polymer solar cells; processing additives

Highly efficient, large area, roll coated flexible and rigid OPV modules with geometric fill factors up to 98.5% processed with commercially available materials - Lucera, L.; Machui, F.; Kubis, P.; Schmidt, H. D.; Adams, J.; Strohm, S.; Ahmad, T.; Forberich, Karen; Egelhaaf, H. -J.; Brabec, Christoph (Energy and Environmental Science, 2016)
Highly efficient, large area OPV modules achieving full area efficiencies of up to 93% of the reference small area cells are reported. The way to a no-loss up-scaling process is highlighted: photoelectrical conversion efficiencies of 5.3% are achieved on rigid modules and of 4.2% on flexible, roll coated ones, employing a commercially available photoactive material. Exceptionally high geometric fill factors (98.5%), achieved via structuring by ultrashort laser pulses, with interconnection widths below 100 μm are demonstrated.
Keywords: Engineering controlled terms: Efficiency; Ultrashort pulses Area efficiency; Fill factor; Photoactive materials; Small area; Upscaling Engineering main heading: Coated materials

Highly efficient, large area, roll coated flexible and rigid solar modules: Design rules and realization - Lucera, Luca; Machui, Florian; Kubis, Peter; Egelhaaf, Hans Joachim; Brabec, Christoph (43rd IEEE Photovoltaic Specialists Conference, PVSC 2016, Category numberCFP16PSC-ART; Code 124913, 2016)
Large area, roll-to-roll printed solar modules are presented in literature with power conversion efficiencies (PCE) well below hero solar cells produced in the lab. Here we show how to design a proper layout to minimize the electrical losses and how to evaluate optical losses induced by the substitution of the sputtered/evaporated electrodes with solution processable ones. Highly efficient, large area, roll-produced solar modules are then shown, achieving PCEs above 4.2% on total area on flexible and of 5.3% on glass substrates. A record-breaking geometric fill factor of 98.5% is demonstrated, thanks to ultra-fast laser structurin
Keywords: large area modules; no losses; organic photovoltaics; printed photovoltaics; Simulation

Highly efficient, large area, roll coated flexible and rigid solar modules: Design rules and realization - Lucera, Luca; Machui, Florian; Kubis, Peter; Egelhaaf, Hans-J.; Brabec, Christoph (44th IEEE Photovoltaic Specialist Conference, PVSC 2017; Category numberCFP17PSC-ART; Code 136737, 2018)
Large area, roll-to-roll printed solar modules are presented in literature with power conversion efficiencies (PCE) well below hero solar cells produced in the lab. Here we show how to design a proper layout to minimize the electrical losses and how to evaluate optical losses induced by the substitution of the sputtered/evaporated electrodes with solution processable ones. Highly efficient, large area, roll-produced solar modules are then shown, achieving PCEs above 4.2% on total area on flexible and of 5.3% on glass substrates. A record-breaking geometric fill factor of 98.5% is demonstrated, thanks to ultra-fast laser structurin
Keywords: Large area modules; No losses; Organic photovoltaics; Printed photovoltaics; Simulation

Highly efficient organic solar cells based on a simple polymer donor derived from a difluorinated benzene-quarterthiophene skeleton - Zhang, Zesheng; Kong, Lingchen; Liu, Chao; Tang, Hua; Wang, Xinkang; Chen, Mingqing; Luo, Mei; Zhang, Lianjie; Liu, Cheng; Liu, Xuncheng; Ma, Dongge; Brabec, Christoph; et al. (Journal of Materials Chemistry C, 2025)
Conjugated polymers with simple chemical structures are essential for the commercialization of organic solar cells (OSCs). However, a simplicity-performance dilemma arises, as current design principles often result in an inverse correlation between these two factors, significantly hindering the commercialization of OSCs. In this study, we investigated the impact of fluorine substitution positions on benzene rings within polythiophenes (PTs), leading to two polymers composed of non-fused rings of o-difluorobenzene-quarterthiophene and p-difluorobenzene-quarterthiophene, namely, Po2F and Pp2F. The Po2F/Y6BO devices achieved a remarkable efficiency of 15.45%, with the active layer fabricated via layer-by-layer (LBL) spin coating, significantly surpassing the Pp2F/Y6BO blend (12.14%) and ranking among the top-performing oligothiophene-based OSCs. The enhancement is mainly attributed to improved phase separation, reduced exciton lifetimes, and suppressed mixing compatibility with Y6BO of Po2F, compared to Pp2F. In addition, the simple polymer Po2F demonstrated a much higher figure of merit (FOM) in chemical accessibility than polymers with fused rings, indicating its great potential for cost reduction. Beyond its role as a donor, Po2F also enhanced the efficiency of PM6:L8BO from 17.74% to 19.05% and extended T80 from 239 to 377 hours when used as an interlayer between the PEDOT:PSS buffer layer and the active layer. This study highlights the significance of a polymer donor-based non-fused ring towards commercially viable OSCs and offers valuable insights for designing high-performance polymers.
CRIS-Team Scopus Importer:2025-04-01

Highly efficient organic tandem solar cells: A follow up review - Ameri, Tayebeh; Li, Ning; Brabec, Christoph (Energy and Environmental Science, 2013)
Multi-junction solar cell configurations, where two or further sub-cells with complementary absorption are stacked and connected in series or parallel, offer an exciting approach to tackle the single junction limitations of organic solar cells and further improve their power conversion efficiency. In this article we aim to follow up our previous work and review the most important and novel developments that have been recently reported on organic tandem solar cells. In addition, some brief theoretical considerations addressing the potential of single and tandem solar cells, the working principles of the intermediate layer, the importance and benefits of optical simulations and finally the intricacies of a precise performance measurement of bulk-heterojunction organic tandem solar cells based on complementary absorber materials are presented. © 2013 The Royal Society of Chemistry.
Keywords: Bulk heterojunction; Intermediate layers; Multi junction solar cells; Optical simulation; Organic solar cell; Performance measurements; Power conversion efficiencies; Tandem solar cells Engineering controlled terms: Heterojunctions Engineering main heading: Solar cells GEOBASE Subject Index: energy efficiency; optical method; performance assessment; solar power; solar radiation; theoretical study

Highly Efficient Photocatalytic Hydrogen Evolution Using a Self-Assembled Octupolar Molecular System - Lee, Hyun-Jun; Abudulimu, Abasi; Carlos Roldao, Juan; Nam, Hyunwoo; Gierschner, Johannes; Lüer, Larry; Park, Soo Young (Chemphotochem, 2022)
A highly efficient photocatalytic hydrogen evolution system was prepared by using an octupolar molecule as a building block of self-assembled nanoparticles. The photocatalytic system showed an enhanced hydrogen evolution reaction (HER) rate upon the addition of halide ions, which was attributed to an external heavy atom effect enhancing intersystem crossing. The HER rate of the photocatalytic system was proportional to the atomic weight and concentration of halide ion additives, and its maximum HER rate reached 460 mmol/g ⋅ h in the presence of iodide ions and a metal co-catalyst. Further, the photocatalytic system without any halide ion additives generated hydrogen gas utilizing seawater and stimulated sunlight with remarkable efficiency (apparent quantum yield∼3.8 %).
CRIS-Team Scopus Importer:2022-10-21
Keywords: hydrogen evolution; intersystem crossing; photocatalysis; self-assembly; water splitting

Highly luminescent Ca3Sc2Si3O12:Ce3+ silicate garnet nano- and microparticles with 50-70% photoluminescence quantum yields as efficient phosphor converters for white LEDs - Levchuk, Ievgen; Schröppel, Felix; Römling, Lukas; Chepyga, Liudmyla; Osvet, Andres; Khaidukov, Nicholas; Zorenko, Yuriy; Van Deun, Rik; Brabec, Christoph; Batentschuk, Miroslaw (Advanced Materials - TechConnect Briefs 2017, 2017)
We present a novel synthesis method of Ca3Sc2Si3O12:Ce3+ nano- and microparticles with outstandingly bright photoluminescence. Nanoparticles were synthesized by the co-precipitation method, where a long-chain fatty acid salt was used as the precipitation agent for Ca, Sc and Ce water solutions in combination with SiO2 nanoparticles or TEOS as a silica source. Further calcination in reducing atmosphere results in brightly luminescent Ca3Sc2Si3O12:Ce3+ nanopowders with up to 50% photoluminescence quantum yield (PLQY). The modified conventional solid-state reaction was utilized for synthesizing microparticles. Pre-synthesis of metal and silicon oxide solid blends with subsequent high-temperature post-treatment enables to obtain Ca3Sc2Si3O12:Ce3+ microparticles with the record-high PLQY of about 70%. Additionally, both kinds of samples display significantly higher thermal stability of photoluminescence in comparison to a commercial YAG:Ce phosphor.
Keywords: Ca3Sc2Si3O12:Ce3+; Co-precipitation; Nanopowder; Phosphor converter; White LED

Highly Luminescent, Size- and Shape-Tunable Copper Indium Selenide Based Colloidal Nanocrystals - Yarema, Olesya; Bozyigit, Deniz; Rousseau, Ian; Nowack, Lea; Yarema, Maksym; Heiß, Wolfgang; Wood, Vanessa (Chemistry of Materials, 2013)
We report a simple, high-yield colloidal synthesis of copper indium selenide nanocrystals (CISe NCs) based on a silylamide-promoted approach. The silylamide anions increase the nucleation rate, which results in small-sized NCs exhibiting high luminescence and constant NC stoichiometry and crystal structure regardless of the NC size and shape. In particular, by systematically varying synthesis time and temperature, we show that the size of the CISe NCs can be precisely controlled to be between 2.7 and 7.9 nm with size distributions down to 9-10%. By introducing a specific concentration of silylamide-anions in the reaction mixture, the shape of CISe NCs can be preselected to be either spherical or tetrahedral. Optical properties of these CISe NCs span from the visible to near-infrared region with peak luminescence wavelengths of 700 to 1200 nm. The luminescence efficiency improves from 10 to 15% to record values of 50-60% by overcoating as-prepared CISe NCs with ZnSe or ZnS shells, highlighting their potential for applications such as biolabeling and solid state lighting.
Keywords: copper indium selenide; CISe nanocrystals; size and shape control; quantum dot colloids; luminescence; lighting applications

Highly Luminescent Transparent Cs2AgxNa1-xBiyIn1-yCl6 Perovskite Films Produced by Single-Source Vacuum Deposition - Stroyuk, Oleksandr; Raievska, Oleksandra; Sebastia-Luna, Paz; Huisman, Bas A.H.; Kupfer, Christian; Barabash, Anastasia; Hauch, Jens; Bolink, Henk J.; Brabec, Christoph J. (ACS Materials Letters, 2023)
Thermal deposition of halide perovskites as a universal and scalable route to transparent thin films becomes highly challenging in the case of lead-free double perovskites, requiring the evaporation dynamics of multiple metal halide sources to be balanced or a single-phase precursor preliminary synthesized to achieve a reliable control over the composition and the phase of the final films. In the present Letter, the feasibility of the single-source vacuum deposition of microcrystalline Cs2AgxNa1-xBiyIn1-yCl6 double perovskites into corresponding transparent nanocrystalline films while preserving the bulk spectral and structural properties is shown. The perovskite films produced from the most emissive powders with x = 0.40 and y = 0.01 revealed a photoluminescence quantum yield of 85%, highlighting thermal evaporation as a promising approach to functional perovskite-based optical materials.
CRIS-Team Scopus Importer:2023-02-03

Highly Reflective and Low Resistive Top Electrode for Organic Solar Cells and Modules by Low Temperature Silver Nanoparticle Ink - Tam, Kai Cheong; Saito, Hirotoshi; Maisch, Philipp; Forberich, Karen; Feroze, Sarmad; Hisaeda, Yutaka; Brabec, Christoph J.; Egelhaaf, Hans-Joachim (Solar RRL, 2021)
One of the issues that have caused a wide performance gap between commercially available organic photovoltaic (OPV) modules and the hero cells in literature lies in the lack of printable and roll-to-roll process compatible high-performance top electrodes. This work takes an unorthodox approach to this issue by developing a printable silver nanoparticle (AgNP) film top electrode that can achieve a similar performance as evaporated ones (EvapAg). It illustrates the developmental process from ink formulation to the critical processing conditions that are tailored for OPV devices procedurally. The resultant cells and modules with AgNP electrodes have achieved almost the same power conversion efficiencies (≈90%) as those with evaporated silver electrodes, as demonstrated for multiple material systems, printing methods, as well as layouts. Under low light condition, AgNP cells perform even significantly better than EvapAg ones, due to their lower leakage currents. More importantly, this work has demonstrated that fully printed OPV modules can achieve similar performance as small scale OPV cells with evaporated electrodes when both the electrical and optical performance of their top electrodes are comparable. With the latest generation of materials, this approach offers an attractive alternative for manufacturing of highly efficient OPV modules at large scale.
CRIS-Team Scopus Importer:2021-12-17
Keywords: inkjet printing; organic photovoltaics; organic solar modules; printed photovoltaics; silver nanoparticles; upscaling

Highly self-ordered nanochannel TiO2 structures by anodization in a hot glycerol electrolyte - Lee, Kiyoung; Kim, Dam-Hee; Schmuki, Patrik (Chemical Communications, 2011)
In the present work, we report on the self-organized growth of TiO2 layers consisting of a highly aligned nanochannel morphology. We show that an electrochemical anodization process of Ti in a hot glycerol/K2HPO4 electrolyte can be adjusted to yield these self-organized TiO2 structures. The channel diameter and length are controllable by the anodization parameters. This directional structure can, for example, find application in dye-sensitized solar cells.
EAM Import::2019-03-13

Highly Stable Lasing from Solution-Epitaxially Grown Formamidinium-Lead-Bromide Micro-Resonators - Afify, Hany A.; Sytnyk, Mykhailo; Rehm, Viktor; Barabash, Anastasia; Mashkov, Oleksandr; Osvet, Andres; Volobuev, Valentine V.; Korczak, Jędrzej; Szczerbakow, Andrzej; Story, Tomasz; Götz, Klaus; Unruh, Tobias; et al. (Advanced Optical Materials, 2022)
High-quality epitaxial growth of oriented microcrystallites on a semiconductor substrate is demonstrated here for formamidinium lead bromide perovskite, by drop casting of precursor solutions in air. The microcrystallites exhibit green photoluminescence at room temperature, as well as lasing with low thresholds. Lasing is observed even though the substrate is fully opaque at the lasing wavelengths, and even though it has a higher refractive index as the perovskite active material. Moreover, the lasing is stable for more than 109 excitation pulses, which is more than what is previously achieved for devices kept in the air. Such highly stable lasing under pulsed excitation represents an important step towards continuous mode operation or even electrical excitation in future perovskite-based devices.
CRIS-Team Scopus Importer:2022-04-14
Keywords: halide perovskites; lasing; microresonators; solution epitaxy

Highly Stable n–i–p Structured Formamidinium Tin Triiodide Solar Cells through the Stabilization of Surface Sn2+ Cations - Hu, Manman; Risqi, Andi Muhammad; Wu, Jianchang; Chen, Liang; Park, Jaewang; Lee, Seung Un; Yun, Hyun Sung; Park, Byung Wook; Brabec, Christoph; Seok, Sang Il (Advanced Functional Materials, 2023)
Improving the performance, reproducibility, and stability of Sn-based perovskite solar cells (PSCs) with n–i–p structures is an important challenge. Spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], a hole transporting material (HTM) with n–i–p structure, requires the oxygen exposure after addition of Li-TFSI [Lithium bis(trifluoromethanesulfonyl)imide] as a dopant to increase the hole concentration. In Sn-based PSC, Sn2+ is easily oxidized to Sn4+ under such a condition, resulting in a sharp decrease in efficiency. Herein, a formamidinium tin triiodide (FASnI3)-based PSCs fabricated using DPI-TPFB [4-Isopropyl-4′-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate] instead of Li-TFSI are reported as a dopant in Spiro-OMeTAD. The DPI-TPFB enables the fabrication of PSCs with an efficiency of up to 10.9%, the highest among FASnI3-based PSCs with n–i–p structures. Moreover, ≈80% of the initial efficiency is maintained even after 1,597 h under maximum power point tracking conditions. In particular, the encapsulated device does not show any decrease in efficiency even after holding for 50 h in the 85 °C/85% RH condition. The high efficiency and excellent stability of PSCs prepared by doping with DPI-TPFB are attributed to not only increasing electrical conductivity by acting as a Lewis acid, but also stabilizing Sn2+ through coordination with Sn2+ on the surface of FASnI3.
CRIS-Team Scopus Importer:2023-04-21
Keywords: efficiency; new dopants; n–i–p structure; oxidation; pure tin perovskite; Spiro-OMeTAD; stability

Highly transmissive luminescent down-shifting layers filled with phosphor particles for photovoltaics - Solodovnyk, Anastasiia; Forberich, Karen; Stern, Edda; Krc, Janez; Topic, Marko; Batentschuk, Miroslaw; Lipovsek, Benjamin; Brabec, Christoph (Optical Materials Express, 2015)
We study the optical properties of polymer layers filled with phosphor particles in two aspects. First, we used two different polymer binders with refractive indices n = 1.46 and n = 1.61 (λ = 600 nm) to study the influence of Δn with the phosphor particles (n = 1.81). Second, we prepared two particle size distributions D = 12 μm and D = 19 μm. The particles were dispersed in both polymer binders in several volume concentrations and coated with thicknesses of 150-600 μm onto glass substrates. Experimental results and numerical simulations show that the layers of the higher refractive index binder with larger particles result in the highest optical transmittance in the visible light spectrum. Finally, we used numerical simulations to determine optimal layer composition for application in realistic photovoltaic devices.
Keywords: Engineering controlled terms: Binders; Bins; Light emission; Numerical models; Optical properties; Particle size; Phosphors; Polymers; Refractive index; Substrates Glass substrates; Layer composition; Phosphor particles; Photovoltaic devices; Photovoltaics; Polymer binders; Polymer layers; Volume concentration Engineering main heading: Filled polymers

Highly transmissive luminescent down-shifting layers filled with phosphor particles for photovoltaics: Publisher's note - Solodovnyk, Anastasiia; Forberich, Karen; Stern, Edda; Krc, Janez; Topic, Marko; Batentschuk, Miroslaw; Lipovsek, Benjamin; Brabec, Christoph (Optical Materials Express, 2015)
This publisher's note amends the author list and Acknowledgments of [Opt. Mater. Express 5, 1296 (2015)]. The author names were corrected online as of June 24, 2015: https://www.osapublishing.org/ome/abstract.cfm?uri=ome-5-6-1296.

High Mobility and Low Density of Trap States in Dual-Solid-Gated PbS Nanocrystal Field-Effect Transistors - Nugraha, Mohamad Insan; Häusermann, Roger; Bisri, Satria Zulkarnaen; Matsui, Hiroyuki; Sytnyk, Mykhailo; Heiß, Wolfgang; Takeya, Jun; Loi, Maria Antonietta (Advanced Materials, 2015)
Dual-gated PbS nanocrystal field-effect transistors employing SiO and Cytop as gate dielectrics are fabricated. The obtained electron mobility (0.2 cm V s) and the high on/off ratio (10-10), show that the controlled nanocrystal assembly (obtained with self-assembled monolayers), as well as the trap density reduction (using Cytop as dielectric), are crucial steps for the future application of nanocrystals.
Keywords: Ambipolar transistors; Colloidal nanocrystals; Density of trap states; Field effect transistors

High Performance All-Polymer Photodetector Comprising a Donor- Acceptor-Acceptor Structured Indacenodithiophene-Bithieno[3,4-c]Pyrroletetrone Copolymer - Murto, Petri; Genene, Zewdneh; Benavides, Cindy Montenegro; Xu, Xiaofeng; Sharma, Anirudh; Pan, Xun; Schmidt, Oliver; Brabec, Christoph; Andersson, Mats R.; Tedde, Sandro F.; Mammo, Wendimagegn; Wang, Ergang (ACS Macro Letters, 2018)
The synthesis of an acceptor polymer PIDT-2TPD, comprising indacenodithiophene (IDT) as the electron-rich unit and an interconnected bithieno[3,4-c]-pyrrole-4,4',6,6'-tetrone (2TPD) as the electron-deficient unit, and its application for all-polymer photodetectors is reported. The optical, electrochemical, charge transport, and device properties of a blend of poly(3-hexylthiophene) and PIDT-2TPD are studied. The blend shows strong complementary absorption and balanced electron and hole mobility, which are desired properties for a photoactive layer. The device exhibits dark current density in the order of 10(-5) mA/ cm(2), external quantum efficiency broadly above 30%, and nearly planar detectivity over the entire visible spectral range (maximum of 1.1 x 10(12) Jones at 610 nm) under -5 V bias. These results indicate that PIDT-2TPD is a highly functional new type of acceptor and further motivate the use of 2TPD as a building block for other n-type materials.

High-performance all-polymer solar cells with only 0.47 eV energy loss - Wu, Qiang; Wang, Wei; Wang, Tao; Sun, Rui; Guo, Jing; Wu, Yao; Jiao, Xuechen; Brabec, Christoph; Li, Yongfang; Min, Jie (Science China-Chemistry, 2020)
The field of all-polymer solar cells (all-PSCs) has experienced rapid development during the past few years, mainly driven by the development of efficient polymer acceptors. However, the power conversion efficiencies (PCEs) of the all-PSCs are still limited by insufficient light absorption of the donor/acceptor blend and large energy loss in devices. We herein designed a polymer acceptor PYT1 constructed n-type molecular acceptor Y5-C20 as the key building block and blended it with a polymer donor PM6 to obtain an all-polymer photoactive layer. The optimized PM6:PYT1 all-PSCs achieved a record higher PCE of 13.43% with a very low energy loss of 0.47 eV and a photoresponse of up to 900 nm compared with the Y5-C20 based device with a best PCE of 9.42%. Furthermore, the PCEs of the PM6:PYT1 all-PSCs are relatively insensitive to the 1-chloronaphthalene (CN) additive contents and active layer thickness. Our results also highlight the effect of CN additive on PM6:PYT1 morphology, i.e., charge generation, and transport find an optimized balance, and radiative and non-radiative loss is simultaneously reduced in the blend. This work promotes the development of high-performance polymer acceptors and heralds a brighter future of all-PSCs for commercial applications.
CRIS-Team Scopus Importer:2020-07-17
Keywords: absorption coefficient; all-polymer solar cells; energy loss; mechanical stability; polymer acceptor

High performance all-small-molecule solar cells: Engineering the nanomorphology: Via processing additives - Min, Jie; Kwon, Oh Kyu; Cui, Chaohua; Park, Jung-Hwa; Wu, Yue; Park, Soo Young; Li, Yongfang; Brabec, Christoph (Journal of Materials Chemistry A, 2016)
The use of small volumes of solvent additives (SAs) or little amounts of non-volatile additives is a processing approach that has been implemented in many high/record performing bulk heterojunction (BHJ) organic solar cells (OSCs). Here, the effects of six SA systems and a molecular additive di-2-thienyl-2,1,3-benzothiadiazole (DTBT) were studied with respect to the photovoltaic parameters of solution-processed all small molecule solar cells (all-SMSCs) based on the BDTT-S-TR:NIDCS-MO system. An effective strategy with binary additives has been employed in this all-SM system, where a small amount, 0.75 vol% 1,8-diiodooctane (DIO) and 2 wt% DTBT were added to the casting solution. This efficient SA approach yielded the highest power conversion efficiency (PCE) of 5.33%. The relevant additives facilitate phase separation in the nm domains and improve bulk transport as evidenced by photoluminescence (PL), atomic force microscopy (AFM), X-ray diffraction (XRD) and space charge limited current (SCLC) measurements.
Keywords: Engineering controlled terms: Additives; Atomic force microscopy; Cell engineering; Heterojunctions; Molecules; Organic solar cells; Phase separation; Photovoltaic effects; Solar power generation; X ray diffraction 1; 3-benzothiadiazole; Bulk heterojunction (BHJ); Molecular additives; Photovoltaic parameters; Power conversion efficiencies; Processing approach; Solution-processed; Space-charge-limited current Engineering main heading: Solar cells

High-performance direct conversion X-ray detectors based on sintered hybrid lead triiodide perovskite wafers - Shrestha, Shreetu; Fischer, Rene; Matt, Gebhard; Feldner, Patrick; Michel, Thilo; Osvet, Andres; Levchuk, Ievgen; Merle, Benoit; Golkar, Saeedeh; Chen, Haiwei; Tedde, Sandro F.; Schmidt, Oliver; et al. (Nature Photonics, 2017)
Lead halide perovskite semiconductors are in general known to have an inherently high X-ray absorption cross-section and a significantly higher carrier mobility than any other low-temperature solution-processed semiconductor. So far, the processing of several-hundred-micrometres-thick high-quality crystalline perovskite films over a large area has been unresolved for efficient X-ray detection. In this Article, we present a mechanical sintering process to fabricate polycrystalline methyl ammonium lead triiodide perovskite (MAPbI(3)) wafers with millimetre thickness and well-defined crystallinity. Benchmarking of the MAPbI(3) wafers against state-of-the-art CdTe detectors reveals competitive conversion efficiencies of 2,527 mu C Gy(air)(-1) cm(-2) under 70 kV(p) X-ray exposure. The high ambipolar mobility-lifetime product of 2 x 10(-4) cm(2) V-1 is suggested to be responsible for this exceptionally high sensitivity. Our findings inform a new generation of highly efficient and low-cost X-ray detectors based on perovskite wafer

High-Performance Organic Photodetectors from a High-Bandgap Indacenodithiophene-Based π-Conjugated Donor-Acceptor Polymer. - Benavides, Cindy Montenegro; Murto, Petri; Chochos, Christos L.; Gregoriou, Vasilis G.; Avgeropoulos, Apostolos; Xu, Xiaofeng; Bini, Kim; Sharma, Anirudh; Andersson, Mats R.; Schmidt, Oliver; Brabec, Christoph; Wang, Ergang; et al. (ACS Applied Materials and Interfaces, 2018)
A conjugated donor-acceptor polymer, poly[4,4,9,9-tetrakis (4-hexylpheny1)-4,9-dihydro-s-in dace no [1,2-b: 5,6-b']dithiophene 2,7 diyl alt-5 (2-ethylhexyl)-4H-thieno[3,4-c] pyrrole-4,6 (5H)-dione-1,3-diyl](PIDT-TPD), is blended with the fullerene derivative [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) for the fabrication of thin and solution-processed organic photodetectors (OPDs). Systematic screening of the concentration ratio of the blend and the molecular weight of the polymer is performed to optimize the active layer morphology and the OPD performance. The device comprising a medium molecular weight polymer (27.0 kg/mol) in a PIDT-TPD:PC61BM 1:1 ratio exhibits an external quantum efficiency of 52% at 610 nm, a dark current density of 1 nA/cm(2), a detectivity of 1.44 x 10(13) Jones, and a maximum 3 dB cutoff frequency of 100 kHz at -5 V bias. These results are remarkable among the state-of-the-art red photodetectors based on conjugated polymers. As such, this work presents a functional organic active material for high-speed OPDs with a linear photoresponse at different light intensities.
Keywords: concentration ratio; dark current density; frequency response; high speed; molecular weight; red organic photodetectors

High-Performance Organic Solar Cells Based on a Small Molecule with Alkylthio-Thienyl-Conjugated Side Chains without Extra Treatments - Cui, Chaohua; Guo, Xia; Min, Jie; Guo, Bing; Cheng, Xiao; Zhang, Maojie; Brabec, Christoph; Li, Yongfang (Advanced Materials, 2015)
A new 2D-conjugated small molecule with alkylthio-thienyl-conjugated side chains (BDTT-S-TR) is synthesized for application as a donor material in organic solar cells (OSCs). The OSCs based on BDTT-S-TR/PCBM demonstrate a power conversion efficiency (PCE) of 9.20% without extra treatment. Moreover, an encouraging PCE of 6.68% is achieved from the device with active area of 144 mm.
Keywords: conjugated side chains; organic molecules; organic solar cells; solution processability

High-performance semitransparent perovskite solar cells with solution-processed silver nanowires as top electrodes - Guo, Fei; Azimi, Seyed Hamed; Hou, Yi; Przybilla, Thomas; Hu, Mengyao; Bronnbauer, Carina; Langner, Stefan; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (Nanoscale, 2015)
In this work, we report efficient semitransparent perovskite solar cells using solution-processed silver nanowires (AgNWs) as top electrodes. A thin layer of zinc oxide nanoparticles is introduced beneath the AgNWs, which fulfills two essential functionalities: it ensures ohmic contact between the PC60BM and the AgNWs and it serves as a physical foundation that enables the solution-deposition of AgNWs without causing damage to the underlying perovskite. The as-fabricated semitransparent perovskite cells show a high fill factor of 66.8%, V-oc = 0.964 V, J(sc) = 13.18 mA cm(-2), yielding an overall efficiency of 8.49% which corresponds to 80% of the reference devices with reflective opaque electrode

High performance tandem organic solar cells via a strongly infrared-absorbing narrow bandgap acceptor - Jia, Zhenrong; Qin, Shucheng; Meng, Lei; Ma, Qing; Angunawela, Indunil; Zhang, Jinyuan; Li, Xiaojun; He, Yakun; Lai, Wenbin; Li, Ning; Ade, Harald; Brabec, Christoph; et al. (Nature Communications, 2021)
Tandem organic solar cells are based on the device structure monolithically connecting two solar cells to broaden overall absorption spectrum and utilize the photon energy more efficiently. Herein, we demonstrate a simple strategy of inserting a double bond between the central core and end groups of the small molecule acceptor Y6 to extend its conjugation length and absorption range. As a result, a new narrow bandgap acceptor BTPV-4F was synthesized with an optical bandgap of 1.21 eV. The single-junction devices based on BTPV-4F as acceptor achieved a power conversion efficiency of over 13.4% with a high short-circuit current density of 28.9 mA cm−2. With adopting BTPV-4F as the rear cell acceptor material, the resulting tandem devices reached a high power conversion efficiency of over 16.4% with good photostability. The results indicate that BTPV-4F is an efficient infrared-absorbing narrow bandgap acceptor and has great potential to be applied into tandem organic solar cells.
CRIS-Team Scopus Importer:2021-01-15

High performance ternary organic solar cells with thick active layer exceeding 11% efficiency - Gasparini, Nicola; Lucera, Luca; Salvador, Michael Filipe; Prosa, Mario; Spyropoulos, Georgios; Kubis, Peter; Egelhaaf, Hans Joachim; Brabec, Christoph; Ameri, Tayebeh (Energy and Environmental Science, 2017)
We present a novel ternary organic solar cell with uncommonly thick active layer (>300 nm), featuring thickness invariant charge carrier recomb ination and delivering 11% power conversion efficiency (PCE). The ternary blend was used to demonstrate photovoltaic modules of high technological relevance both on gla ss and flexible substrates, yielding 8.2% and 6.8% PCE, respectively.

High-Performance Thick-Film All-Polymer Solar Cells Created Via Ternary Blending of a Novel Wide-Bandgap Electron-Donating Copolymer - Fan, Baobing; Zhu, Peng; Xin, Jingming; Li, Ning; Ying, Lei; Zhong, Wenkai; Li, Zhenye; Ma, Wei; Huang, Fei; Cao, Yong (Advanced Energy Materials, 2018)
A novel wide-bandgap electron-donating copolymer containing an electrondeficient, difluorobenzotriazole building block with a siloxane-terminated side chain is developed. The resulting polymer, poly(4,8-bis(4,5-dihexylthiophen2- yl) benzo[1,2-b: 4,5-b'] dithiophene-co-4,7-di(thiophen-2-yl)-5,6-difluoro-2-(6( 1,1,1,3,5,5,5-heptamethyltri-siloxan-3-yl) hexyl)-2H-benzo[d][1,2,3] triazole (PBTA-Si), is used to successfully fabricate high-performance, ternary, all-polymer solar cells (all-PSCs) insensitive to the active layer thickness. An impressively high fill factor of approximate to 76% is achieved with various ternary-blending ratios. The optimized all-PSCs attain a power conversion efficiency (PCE) of 9.17% with an active layer thickness of 350 nm and maintain a PCE over 8% for thicknesses over 400 nm, which is the highest reported efficiency for thick all-PSCs. These results can be attributed to efficient charge transfer, additional energy transfer, high and balanced charge transport, and weak recombination behavior in the photo-active layer. Moreover, the photoactive layers of the ternary all-PSCs are processed in a nonhalogenated solvent, 2-methyltetrahydrofuran, which greatly improves their compatibility with large-scale manufacturing.
Keywords: all-polymer solar cells; high performance; siloxane-functionalized side chains; ternary blends; thick active layers

High Performance X-ray to Current Converters Fabricated Via Sintering or Melting of a Metal-halide Perovskite - Matt, Gebhard; Levchuk, Ievgen; Knüttel, Judith; Shrestha, Shreetu; Dallmann, Johannes; Hock, Rainer; Heiß, Wolfgang; Brabec, Christoph (nanoGe Fall Meeting 2019, 2019)
The search for an ideal X-ray sensitive photo-conductor is an ongoing task since the most semiconductors do not absorb high energy radiation effectively. However, the latter is an intrinsic property of the lead-halide perovskites semiconductors due to high radiation attenuation by the lead and halide ions combined with there good charge transport properties. In this presentation we will review our latest efforts utilizing organic-inorganic (MAPbI3) as well as a pure inorganic metal-halide perovkite (CsPbBr3) for X-ray to current converters. We demonstrate a sintering as well as a melting process which leads to the formation of several hundred µm thick and crystalline samples. Most notable for these samples are the good charge transport properties and unusual high mobility- lifetime products ( 1E-3 cm^2/V). The achieved X-ray to current conversation rate up to 2500 µC/Gycm2 is on par to the current state-of-the-art Cd(Zn)Te detector technology and our findings inform on a low-cost scaleable technology for the next generation of high energy detector technology.

High precision processing of flexible P3HT/PCBM modules with geometric fill factor over 95% - Kubis, Peter; Lucera, Luca; Machui, Florian; Spyropoulos, Georgios; Cordero, Johann; Frey, Alfred; Kaschta, Joachim; Voigt, Monika; Matt, Gebhard; Zeira, Eitan; Brabec, Christoph (Organic Electronics, 2014)
Flexible OPV modules, based on P3HT:PCBM as absorber layer, were manufactured with a power conversion efficiency over 3% and for a total area of 3500 mm(2) consisting of 14 in series interconnected cells. The modules utilize the excellent mechanical and the outstanding optical properties of sputtered transparent ITO-Metal-ITO (IMI) electrodes deposited on the PET foil on the one hand, and the combination of large area slot-die coating with high resolution ultrafast laser patterning on the other hand. The manufacturing of modules with outstanding performance was found to be reproducible. The right combination of innovative electrodes and smart roll-to-roll compatible processing technologies demonstrates a viable path towards high efficient industrial module technology. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Flexible transparent electrode; Flexible OPV module; Slot-die coating; Ultra-fast laser patterning; High geometric fill factor

High Q femtoREGEN™ UC laser systems for industrial microprocessing applications - Matylitsky, V. V.; Kubis, Peter; Brabec, Christoph; Au, J. Aus Der (Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XII, 2012)
High average power, high repetition rate femtosecond lasers with μJ pulse energies are increasingly used for bio-medical and material processing applications. With the introduction of femtosecond laser systems such as the High Q femtoREGEN™ UC platform, micro-processing of solid targets with femtosecond laser pulses have obtained new perspectives for industrial applications. The unique advantage of material processing with sub-picosecond lasers is efficient, fast and localized energy deposition, which leads to high ablation efficiency and accuracy in nearly all kinds of solid materials. In this paper, we will show aspects of the design and performance of the femtoREGEN™ UC industrial laser system and give an overview of actual applications. © 2012 SPI
Keywords: Ablation; Femtosecond laser pulse; Micro-processing; Ultrafast laser

High-Resolution spectroScopic mapping of the chemical contrast from nanometer domains in P3HT:PCBM organic blend films for Solar-Cell applications by - Wang, Xiao; Zhang, Dai; Braun, Kai; Egelhaaf, Hans-Joachim; Brabec, Christoph; Meixner, Alfred J. (Advanced Functional Materials, 2010)
A high-resolution near-field spectroscopic mapping technique is successfully applied to investigate the influence of thermal annealing on the morphology of a poly(3-hexylthiophene) and [6,6]-penyl-C butyric acid methyl ester (P3HT:PCBM) blend film. Based on the simultaneously recorded morphological and spectroscopic information, the interplay among the blend film morphology, the local P3HT:PCBM molecular distribution, and the P3HT photoluminescence (PL) quenching efficiency are systematically discussed. The PL and Raman signals of the electron donor (P3HT) and acceptor (PCBM) are probed at an optical resolution of approximately 10 nm, which allows the chemical nature of the different domains to be identified directly. In addition, the local PL quenching efficiency, which is related to the electron transfer from P3HT to PCBM, is quantitatively revealed. From these experimental results, it is proposed that high-resolution near-field spectroscopic imaging is capable of mapping the local chemical composition and photophysics of the P3HT:PCB M blends on a scale of a few nanometers. © 2010 WlLEY-VCH Verlag GmbH & Co. KGaA,.

High-sensitivity high-resolution X-ray imaging with soft-sintered metal halide perovskites - Deumel, Sarah; Van Breemen, Albert; Gelinck, Gerwin; Peeters, Bart; Maas, Joris; Verbeek, Roy; Shanmugam, Santhosh; Akkerman, Hylke; Meulenkamp, Eric; Huerdler, Judith E.; Acharya, Manognya; Garcia-Batlle, Marise; et al. (Nature Electronics, 2021)
To realize the potential of artificial intelligence in medical imaging, improvements in imaging capabilities are required, as well as advances in computing power and algorithms. Hybrid inorganic–organic metal halide perovskites, such as methylammonium lead triiodide (MAPbI3), offer strong X-ray absorption, high carrier mobilities (µ) and long carrier lifetimes (τ), and they are promising materials for use in X-ray imaging. However, their incorporation into pixelated sensing arrays remains challenging. Here we show that X-ray flat-panel detector arrays based on microcrystalline MAPbI3 can be created using a two-step manufacturing process. Our approach is based on the mechanical soft sintering of a freestanding absorber layer and the subsequent integration of this layer on a pixelated backplane. Freestanding microcrystalline MAPbI3 wafers exhibit a sensitivity of 9,300 µC Gyair–1 cm–2 with a μτ product of 4 × 10–4 cm2 V–1, and the resulting X-ray imaging detector, which has 508 pixels per inch, combines a high spatial resolution of 6 line pairs per millimetre with a low detection limit of 0.22 nGyair per frame.
CRIS-Team Scopus Importer:2021-10-01

High shunt resistance in polymer solar cells comprising a MoO3 hole extraction layer processed from nanoparticle suspension - Stubhan, Tobias; Ameri, Tayebeh; Salinas Batallas, Michael; Krantz, Johannes; Machui, Florian; Halik, Marcus; Brabec, Christoph (Applied Physics Letters, 2011)
In this report, we present solution processed molybdenum trioxide (MoO3) layers incorporated as hole extraction layer (HEL) in polymer solar cells (PSCs) and demonstrate the replacement of the commonly employed poly(3,4-ethylene dioxythiophene):(polystyrene sulfonic acid) (PEDOT:PSS). MoO3 is known to have excellent electronic properties and to yield more stable devices compared to PEDOT:PSS. We demonstrate fully functional solar cells with up to 65 nm thick MoO3 HEL deposited from a nanoparticle suspension at low temperatures. The PSCs with an active layer comprising a blend of poly(3-hexylthiophene) and [6,6]-phenyl-C61 butyric acid methyl ester and a MoO3 HEL show comparable performance to reference devices with a PEDOT:PSS HEL. The best cells with MoO3 reach a fill factor of 66.7% and power conversion efficiency of 2.92%. Moreover, MoO3 containing solar cells exhibit an excellent shunt behavior with a parallel resistance of above 100 kΩ cm2.

High-speed sequential deposition of photoactive layers for organic solar cell manufacturing - Sun, Rui; Wang, Tao; Yang, Xinrong; Wu, Yao; Wang, Yang; Wu, Qiang; Zhang, Maojie; Brabec, Christoph; Li, Yongfang; Min, Jie (Nature Energy, 2022)
Despite the great success of organic photovoltaics in terms of device efficiency and stability at the laboratory scale, pressing demand for high-throughput and cost-effective solutions remains unresolved and rarely reported. Here we propose that a sequential-deposition, blade-coating approach using donor and acceptor materials can facilitate high-speed fabrication of photoactive layers while maintaining device performance. The sequential-deposition-processed blend and thickness of its designed PM6:T8 system can be optimized by the fine-tuning of the solution concentrations and coating speeds. We show that this strategy can be applied to a non-halogenated solvent and under high-humidity conditions. This high-speed approach is applicable to other non-fullerene photovoltaic systems and the slot-die coating technique. Techno-economic analysis suggests that this strategy can decrease the minimum sustainable price of module manufacturing. Overall, this work represents a step towards the scalable, cost-effective manufacturing of organic photovoltaics with both high performance and high throughput.
CRIS-Team Scopus Importer:2022-11-04

High temperature corrosion of the nickel-based alloy Inconel 617 in helium containing small amounts of impurities - Christ, Hans-Jürgen; Künecke, Ulrike; Meyer, K; Sockel, Hans-Georg (Materials Science and Engineering, 1987)
Application of the technical nickel-based alloy Inconel 617 as a material for gas tubes in the primary circuit of the high temperature gas-cooled reactor is limited essentially by the chemical reactions of the alloying elements with the impurities (CO, CO2, H2, CH4 and H2O) in the helium coolant. Depending on the temperature and gas composition, carburization or decarburization as well as oxidation occur. In this work the interaction of the alloy with the reactive impurities in different simulated cooling gases were investigated by thermogravimetry in a gas-tight microbalance and by simultaneous measurements of the changes in the gas composition by a continuous sensitive mass spectrometry analysis of the gas. The results demonstrate that the occurrence of the various reactions is determined essentially by temperature. For a standardized helium gas (HHT-He), three temperature regions can be distinguished between. Below a critical temperature (about 1105 K) the presence of CO can cause simultaneous oxidation and carburization. Above about 1105 K, this reaction does not reverse itself. Rather, oxidation by CO2 and H2O takes place which shows, after a transient state, the same kinetics as those observed in undiluted oxygen-containing gases. At temperatures above about 1205 K, decarburization of the alloy accompanied by the production of CO takes place, leading to severe destruction of the carbide microstructure and therefore limiting the applicability of the materia
Keywords: Inconel 617; high temperature corrosion

High temperature solution growth of SiC by the vertical Bridgman method using a metal free Si-C-melt at 2300 °C - Fahlbusch, Lars; Schöler, Michael; Mattle, Patrick; Schnitzer, Sarah; Khodamoradi, Hossein; Iwamoto, Naoya; Svensson, Bengt G.; Wellmann, Peter (Materials Science Forum, 2016)
We developed a solution growth process related to the combination of the Vertical Bridgman and Vertical Gradient Freeze in a metal free Si-C melt at growth temperatures of 2300 °C. For this procedure we present a detailed description of the growth process and discuss the influence of different growth parameters on the surface morphology and growth rate. So far, we managed to grow SiC layers with a thickness up to 300 μm. The characterization of the crystal morphology was carried out using SEM images and the metal concentration was estimated using SIM
Keywords: High temperature growth; Metal free; SiC; Solution growth; Surface morphology; Vertical bridgman; Vertical gradient freeze

High-temperature thermographic phosphor mixture YAP/YAG:Dy3+ and its photoluminescence properties - Chepyga, Liudmyla M.; Osvet, Andres; Brabec, Christoph; Batentschuk, Miroslaw (Journal of Luminescence, 2017)
In this work we report on the investigation of high-temperature thermographic phosphors Dy3+-doped yttrium aluminum garnet and the mixture of yttrium aluminum perovskite / yttrium aluminum garnet (YAP/YAG). The phosphors were synthesized by conventional high temperature solid-state method using lithium fluoride (LiF) as a flux. The latter serves also as a source of co-doping Li+ and F- ions affecting the luminescent properties. The photoluminescence intensity of YAP/YAG:Dy (75/25%) mixture was doubled at room temperature compared to YAG:Dy and the intensity ratio of the lines in the regions 450–460 and 480–500 nm was increased from 0.45 to 0.63 at 1293 K, favoring temperature measurements. Therefore, the mixture of YAlO3/Y3Al5O12:Dy is promising material for high temperature phosphor thermometry. © 2017 Elsevier B.V.
Keywords: Aluminum; Dysprosium; Garnets; Light emission; Luminescence; Mixtures; Photoluminescence; Temperature measurement; Thermometers; Yttrium; High temperature solid state methods; Lithium fluoride; Luminescent property; Phosphor thermometry; Photoluminescence intensities; Photoluminescence properties; Thermographic phosphors; Yttrium aluminum garnet; Phosphors

High-Throughput Optical Screening for Efficient Semitransparent Organic Solar Cells - Xia, Ruoxi; Brabec, Christoph; Yip, Hin Lap; Cao, Yong (Joule, 2019)
Power-generating windows for buildings and automobiles bring great photovoltaic market opportunities. Ideal semitransparent photovoltaics should let required visible light pass and convert as much as near-infrared light energy into electric power. However, the current commercial, inorganic, semitransparent photovoltaics cannot fully meet such complex requirements, as their optical properties are intrinsically difficult to tune. Herein, by combining the advantages of organic photovoltaics with highly tunable optical properties and photonic structures with flexible optical regulation, a high-performance device with nearly 11% power conversion efficiency and 30% visible light transmittance was demonstrated. The advanced optical properties of the device were achieved by screening over tens of millions of device configurations through a high-throughput optical model, which had wide potential applications, especially as related to designs including multi-objective and multi-layer thickness optimizations.
CRIS-Team Scopus Importer:2019-09-17
Keywords: computational screening; high-throughput optical model; one-dimensional photonic crystals; semitransparent organic solar cells

High-throughput, outdoor characterization of photovoltaic modules by moving electroluminescence measurements - Doll, Bernd; Pickel, Tobias; Schreer, Oliver; Zetzmann, Cornelia; Hepp, Johannes; Teubner, Janine; Buerhop, Claudia; Hauch, Jens; Camus, Christian; Brabec, Christoph (Optical Engineering, 2019)
Fast and nondestructive quality control tools are important to assess the reliability of photovoltaic plants. On-site inspection is essential to minimize the risk of further damage and electrical yield losses. The most effective way of achieving this is with highly sensitive imaging techniques such as luminescence or infrared thermography imaging. Nowadays, electroluminescence (EL) is used at nighttime to detect defects such as local cell changes, series resistances, and shunts. However, the drawback of this method is low measurement throughput. To increase the throughput, indium gallium arsenide detectors with a resolution of 640 × 512 pixels are used, for which short integration times are possible to acquire EL images. For such short integration times, even moving image acquisition and movie recording are feasible to detect the mentioned defects. An outdoor EL setup is presented for mobile handheld recording, which can even be used under low-light conditions, below 100 W / m2, at daytime. Experiments show that 5 ms integration time is a good compromise between low contrasts for lower integration times and motion blur for higher integration times. The camera prototype has an onboard computer to avoid image transmission losses and an external lithium polymer battery power supply for improved mobility.
CRIS-Team Scopus Importer:2019-09-27
Keywords: defect detection; electroluminescence; high throughput; indium gallium arsenide camera; on-site inspection; photovoltaic module

High throughput, outdoor characterization of silicon photovoltaic modules by moving electroluminescence measurements - Doll, Bernd; Pickel, Tobias; Schreer, Oliver; Zetzmann, Cornelia; Teubner, Janine; Buerhop-Lutz, Claudia; Hauch, Jens; Camus, Christian; Brabec, Christoph (Vol. 10766, 2018)
Fast and non-destructive quality control tools are important to assess the reliability of photovoltaic plants. On-site inspection is essential to minimize the risk of module damage and electrical yield losses. This may only be achieved by using highly sensitive imaging techniques such as luminescence or infrared thermography imaging. Nowadays, electroluminescence is used to detect defects such as local cell changes, series resistances and shunts in solar cells and modules which can cause electrical losses. However, the drawback of this method is the relatively low measurement throughput. To increase the throughput InGaAs cameras with a resolution of 640 x 512 pixels are used, for which low integration times are possible to acquire electroluminescence images. For such low integration times even moving image acquisition and movie recording are feasible to detect the mentioned defects. In this paper, an outdoor electroluminescence setup is presented for mobile handheld recording. Experiments showed that 5 ms integration time is a good compromise between low contrasts for lower integration times and motion blurring for higher integration times. The camera prototype has an onboard computer to avoid image transmission losses. It was controlled and visualized over Wi-Fi and remote desktop connection. The energy supply was provided from LiPo-batteries for improved mobility. In comparison to conventional electroluminescence measurements we can decrease the measurement time of a 20 module string from 5 min to 20 s.<br
Keywords: defect detection; electroluminescence; high throughput; InGaAs camera; on-site inspection; photovoltaic module; InGaAs camera.

High-Throughput Robotic Synthesis and Photoluminescence Characterization of Aqueous Multinary Copper–Silver Indium Chalcogenide Quantum Dots - Stroyuk, Oleksandr; Raievska, Oleksandra; Langner, Stefan; Kupfer, Christian; Barabash, Anastasia; Solonenko, Dmytro; Azhniuk, Yuriy; Hauch, Jens; Osvet, Andres; Batentschuk, Miroslaw; Zahn, Dietrich R. T.; Brabec, Christoph (Particle & Particle Systems Characterization, 2021)
The feasibility of a high-throughput robot-assisted synthesis of complex Cu1-xAgxInSySe1-x (CAISSe) quantum dots (QDs) by spontaneous alloying of aqueous glutathione-capped Ag–In–S, Cu–In–S, Ag–In–Se, and Cu–In–Se QDs is demonstrated. Both colloidal and thin-film core CAISSe and core/shell CAISSe/ZnS QDs are produced and studied by high-throughput semiautomated photoluminescence (PL) spectroscopy. The silver-copper-mixed QDs reveal clear evidence of a band bowing effect in the PL spectra and higher average PL lifetimes compared to the counterparts containing silver or copper only. The photophysical analysis of CAISSe and CAISSe/ZnS QDs indicates a composition-dependent character of the nonradiative recombination in QDs. The rate of this process is found to be lower for mixed copper-silver-based QDs compared to Cu- or Ag-only QDs. The combination of the band bowing effect and the suppressed nonradiative recombination of CAISSe QDs is beneficial for their applications in photovoltaics and photochemistry. The synergy of high-throughput robotic synthesis and a high-throughput characterization in this study is expected to grow into a self-learning synthetic platform for the production of metal chalcogenide QDs for light-harvesting, light-sensing, and light-emitting applications.
CRIS-Team Scopus Importer:2021-09-10
Keywords: combinatorial synthesis; semiconductor nanocrystals; spontaneous alloying; ternary chalcogenides; time-resolved photoluminescence

High-Throughput Time-Resolved Photoluminescence Study of Composition- And Size-Selected Aqueous Ag-In-S Quantum Dots - Stroyuk, Oleksandr; Raievska, Oleksandra; Kupfer, Christian; Solonenko, Dmytro; Osvet, Andres; Batentschuk, Miroslaw; Brabec, Christoph; Zahn, Dietrich R.T. (Journal of Physical Chemistry C, 2021)
Brightly luminescent, composition- and size-selected aqueous Ag-In-S (AIS) and Zn-diffused core/shell AIS/ZnS (ZAIS) quantum dots (QDs) were studied by high-throughput time-resolved photoluminescence (TRPL). Both QD size and QD composition effects on the photophysical properties of AIS (ZAIS) were probed independently by using an automated high-throughput TRPL setup. Linear relationships were found between the average PL lifetimes of AIS and ZAIS QDs and their respective bandgaps (Eg) indicating that the dynamics of the radiative recombination is governed mostly by the energy of the QD excited state irrespective of which factor is varied affecting the QD bandgap, i.e., their size or composition. The rate constants of radiative and nonradiative recombination were evaluated as a function of Eg forming continuous dependences for the entire AIS and ZAIS QD families. The rate of nonradiative recombination increases steeply for smaller QDs with Eg > 2.2 eV for both core AIS and core/shell ZAIS QDs, indicating that the interfacial electron transfer is the major contributor to the observed dependence. A strong decrease of the PL lifetime of AIS (and ZAIS) QDs in dense QD films or QDs incorporated into polyvinylpyrrolidone films was observed as compared to colloidal solutions. A reversible character of this effect upon polymer film dissolution shows that such behavior originates from energy (or electron) transfers among the QDs brought into close contact in the films. This phenomenon is expected to be of significance for the application of ternary QDs as a light-harvesting material.
CRIS-Team Scopus Importer:2021-07-02

Homo-Tandem Polymer Solar Cells with V-OC > 1.8 V for Efficient PV-Driven Water Splitting - Gao, Yangqin; Le Corre, Vincent Marc; Gaïtis, Alexandre; Neophytou, Marios; Hamid, Mahmoud Abdul; Takanabe, Kazuhiro; Beaujuge, Pierre M (Advanced Materials, 2016)

How to Determine a Suitable Alginate for Biofabrication Approaches using an Extensive Alginate Library? - Karakaya, Emine; Schöbel, Lisa; Zhong, Yu; Hazur, Jonas; Heid, Susanne; Forster, Leonard; Tessmar, Joerg; Boccaccini, Aldo R.; Detsch, Rainer (Biomacromolecules, 2023)
Alginate-based hydrogels are a promising class of biomaterials due to their usability, biocompatibility, and high water -binding capacity which is the reason for their broad use in biofabrication. One challenge of these biomaterials is, however, the lack of cell adhesion motifs. This drawback can be overcome by oxidizing alginate to alginate dialdehyde (ADA) and by subsequent cross-linking with gelatin (GEL) to fabricate ADA-GEL hydrogels, which offer improved cell-material interactions. The present work investigates four pharmaceutical grade alginates of different algae sources and their respective oxidized forms regarding their molecular weight and M/G ratio using 1H NMR spectroscopy and gel permeation chromatography. In addition, three different methods for determining the degree of oxidation (% DO) of ADA, including iodometric, spectroscopic, and titration methods, are applied and compared. Furthermore, the aforementioned properties are correlated with the resulting viscosity, degradation behavior, and cell-material interactions to predict the material behavior in vitro and thus choose a suitable alginate for an intended application in biofabrication. In the framework of the present work, easy and practicable detection methods for the investigations of alginate-based bioinks were summarized and shown. In this regard, the success of oxidation of alginate was confirmed by the three aforementioned methods and was further proven by solid-state 13C NMR, for the first time in the literature, that only guluronic acid (G) was attacked during the oxidation, leading to the formation of hemiacetals. Furthermore, it was shown that ADA-GEL hydrogels of alginates with longer G-blocks are more suitable for long-term experiments due to their stability over an incubation period of 21 days, while ADA-GEL hydrogels of alginates with longer mannuronic acid (M)-blocks are more suitable for short-term applications such as sacrificial inks due to their extensive swelling and subsequent loss of shape. Finally, it was proven that the M/G ratio did not show any influence on the biocompatibility or printability of the investigated alginate-based hydrogels. The physicochemical findings provide an alginate library for tailored application in biofabrication.
CRIS-Team WoS Importer:2023-05-05

Hybrid Superconducting-Ferromagnetic [Bi2Sr2(Ca,Y)(2)Cu3O10](0.99)(La2/3Ba1/3MnO3)(0.01) Composite Thick Films - Ricardo Mejia-Salazar, J.; Perea, Jose Dario; Castillo, Roberto; Evelio Diosa, Jesus; Baca, Eval (Materials, 2019)
We report here on the development of composite thick films exhibiting hybrid superconducting and ferromagnetic properties, produced through a low-cost, fast, and versatile process. These films were made of high T-c cuprate superconductor Bi2Sr2(Ca,Y)(2)Cu3O10 (with Y:Ca ratio of 5%) and ferromagnetic perovskite La2/3Ba1/3MnO3, synthesized by melting-quenching annealing process on a MgO substrate. Curie temperature for La2/3Ba1/3MnO3 was determined (similar to 336 K ) by magnetic field assisted thermogravimetric analysis (TGA), while superconducting behavior of Bi2Sr2(Ca,Y)(2)Cu3O10/MgO films was observed through temperature-dependent resistance measurements. Superconducting features in our hybrid compound were corroborated by temperature-dependent resistivity and magnetic susceptibility.
CRIS-Team WoS Importer:2019-04-30

Hydrogen and Corrosion Resistance of Nickel Superalloys for Gas Turbines, Engines Cooled Blades - Balitskii, Alexander I.; Kvasnytska, Yuliia H.; Ivaskevych, Lyubomir M.; Kvasnytska, Kateryna H.; Balitskii, Olexiy A.; Shalevska, Inna A.; Shynskii, Oleg Y.; Jaworski, Jaroslaw M.; Dowejko, Jakub M. (Energies, 2023)
The paper presents the results of the analysis of the resistance to hydrogen and high-temperature salt corrosion of the developed alloy of the CM88Y type for the turbine blades of gas turbine engines for marine and power purposes in comparison with the industrial heat-resistant corrosion-resistant alloy CM88Y and the alloy for the protective coating of the SDP3-A blades. SDP3-A alloy was chosen as a reference sample, which has high hydrogen and corrosion resistance. The new heat-resistant alloy additionally contains such refractory metals as rhenium and tantalum, which are added to the composition of the alloy in order to increase operational characteristics while maintaining phase-structural stability. These are properties such as long-term and fatigue strength, characteristics of plasticity and strength at room and elevated temperatures. Therefore, the purpose of these studies was to determine the resistance to high-temperature salt corrosion of the developed alloy in comparison with the industrial heat-resistant nickel alloy and to evaluate the influence of alloying, hydrogen embrittlement of CM88Y and ZhS3DK alloys with different contents of chromium, boron, zirconium, hafnium, and yttrium were compared. The corrosion resistance of the materials was evaluated after crucible tests in a salt solution at a temperature of 900 °C for 30 h, according to the standard method. The corrosion resistances of alloys were determined by the mass loss, corrosion rate, and data from metallographic studies.
CRIS-Team Scopus Importer:2023-02-24
Keywords: gas turbine engine blade; heat-resistant alloy; high-temperature salt corrosion

Hydrogenated Anatase: Strong Photocatalytic Dihydrogen Evolution without the Use of a Co-Catalyst - Liu, Ning; Schneider, Christopher; Freitag, Detlef; Venkatesan, Uma Maheswari; Marthala, Venkata; Hartmann, Martin; Winter, Benjamin; Spiecker, Erdmann; Osvet, Andres; Zolnhofer, Eva; Meyer, Karsten; Nakajima, Tomohiko; et al. (Angewandte Chemie International Edition, 2014)
The high-pressure hydrogenation of commercially available anatase or anatase/rutile TiO2 powder can create a photocatalyst for H-2 evolution that is highly effective and stable without the need for any additional co-catalyst. This activation effect cannot be observed for rutile; however, for anatase/rutile mixtures, a strong synergistic effect can be found (similar to results commonly observed for noble-metal-decorated TiO2). EPR and PL measurements indicated the intrinsic co-catalytic activation of anatase TiO2 to be due to specific defect centers formed during hydrogenation. These active centers can be observed specifically for high-pressure hydrogenation; other common reduction treatments do not result in this effect.
Keywords: co-catalyst; hydrogenation; titanium(III); TiO2; water splitting

Hydrogen-Bonded Organic Semiconductor Micro- And Nanocrystals: From Colloidal Syntheses to (Opto-)Electronic Devices - Sytnyk, Mykhailo; Glowacki, Eric Daniel; Yakunin, Sergii; Voss, Gundula; Schoefberger, Wolfgang; Kriegner, Dominik; Stangl, Julian; Trotta, Rinaldo; Gollner, Claudia; Tollabimazraehno, Sajjad; Romanazzi, Giuseppe; Bozkurt, Zeynep; et al. (Journal of the American Chemical Society, 2014)
Organic pigments such as indigos, quinacridones, and phthalocyanines are widely produced industrially as colorants for everyday products as various as cosmetics and printing inks. Herein we introduce a general procedure to transform commercially available insoluble microcrystalline pigment powders into colloidal solutions of variously sized and shaped semiconductor micro- and nanocrystals. The synthesis is based on the transformation of the pigments into soluble dyes by introducing transient protecting groups on the secondary amine moieties, followed by controlled deprotection in solution. Three deprotection methods are demonstrated: thermal cleavage, acid-catalyzed deprotection, and amine-induced deprotection. During these processes, ligands are introduced to afford colloidal stability and to provide dedicated surface functionality and for size and shape control. The resulting micro- and nanocrystals exhibit a wide range of optical absorption and photoluminescence over spectral regions from the visible to the near-infrared. Due to excellent colloidal solubility offered by the ligands, the achieved organic nanocrystals are suitable for solution processing of (opto)electronic devices. As examples, phthalocyanine nanowire transistors as well as quinacridone nanocrystal photodetectors, with photoresponsivity values by far outperforming those of vacuum deposited reference samples, are demonstrated. The high responsivity is enabled by photoinduced charge transfer between the nanocrystals and the directly attached electron-accepting vitamin B2 ligands. The semiconducting nanocrystals described here offer a cheap, nontoxic, and environmentally friendly alternative to inorganic nanocrystals as well as a new paradigm for obtaining organic semiconductor materials from commercial colorants.
Keywords: Charge transfer; Hydrogen bonds; Infrared devices; Ligands; Light absorption; Nanowires; Nematic liquid crystals; Nitrogen compounds; Pigments; Semiconductor devices; Thermoelectric equipment Absorption and photoluminescence; Environmentally friendly alternatives; Inorganic nanocrystals; Nanocrystals; Nanowire transistors; Organic nanocrystals; Photoinduced charge transfer; Semiconducting nanocrystals; Surface functionalities

Hydrogen-Bonded Organic Semiconductors as Stable Photoelectrocatalysts for Efficient Hydrogen Peroxide Photosynthesis - Jakesova, Marie; Apaydin, Dogukan Hazar; Sytnyk, Mykhailo; Oppelt, Kerstin; Heiß, Wolfgang; Sariciftci, Niyazi Serdar; Glowacki, Eric Daniel; Heiß, Wolfgang (Advanced Functional Materials, 2016)
Research on semiconductor photocatalysts for the conversion of solar energy into chemical fuels has been at the forefront of renewable energy technologies. Water splitting to produce H and CO reduction to hydrocarbons are the two prominent approaches. A lesser-known process, the conversion of solar energy into the versatile high-energy product HO via reduction of O has been proposed as an alternative concept. Semiconductor photoelectrodes for the direct photosynthesis of HO from O have not been applied up to now. Photoelectrocatalytic oxygen reduction to peroxides in aqueous electrolytes by hydrogen-bonded organic semiconductor is observed photoelectrodes. These materials have been found to be remarkably stable operating in a photoelectrochemical cell converting light into HO under constant illumination for at least several days, functioning in a pH range from 1 to 12. This is the first report of a semiconductor photoelectrode for HO production, with catalytic performance exceeding prior reports on photocatalysts by one to two orders of magnitude in terms of peroxide yield/catalyst amount/time. The combination of a strongly reducing conduction band energy level with stability in aqueous electrolytes opens new avenues for this widely available materials class in the field of photo(electro) catalysis.
Keywords: Engineering controlled terms: Carbon dioxide; Catalysis; Electrolytes; Electrolytic reduction; Hydrogen peroxide; Oxidation; Peroxides; Photocatalysis; Photoelectrochemical cells; Photosynthesis; Reduction; Renewable energy resources; Semiconducting organic compounds; Solar energy Alternative concepts; Catalytic performance; Conduction band energy levels; Photoelectrocatalysts; Photoelectrocatalytic; Renewable energy technologies; Semiconductor photocatalyst; Semiconductor photoelectrode Engineering main heading: Hydrogen bonds

Hypericin-bearing magnetic iron oxide nanoparticles for selective drug delivery in photodynamic therapy - Unterweger, Harald; Subatzus, Daniel; Tietze, Rainer; Janko, Christina; Poettler, Marina; Stiegelschmitt, Alfons; Schuster, Matthias; Maake, Caroline; Boccaccini, Aldo R.; Alexiou, Christoph (International Journal of Nanomedicine, 2015)
Combining the concept of magnetic drug targeting and photodynamic therapy is a promising approach for the treatment of cancer. A high selectivity as well as significant fewer side effects can be achieved by this method, since the therapeutic treatment only takes place in the area where accumulation of the particles by an external electromagnet and radiation by a laser system overlap. In this article, a novel hypericin-bearing drug delivery system has been developed by synthesis of superparamagnetic iron oxide nanoparticles (SPIONs) with a hypericin-linked functionalized dextran coating. For that, sterically stabilized dextran-coated SPIONs were produced by coprecipitation and crosslinking with epichlorohydrin to enhance stability. Carboxymethylation of the dextran shell provided a functionalized platform for linking hypericin via glutaraldehyde. Particle sizes obtained by dynamic light scattering were in a range of 55-85 nm, whereas investigation of single magnetite or maghemite particle diameter was performed by transmission electron microscopy and X-ray diffraction and resulted in approximately 4.5-5.0 nm. Surface chemistry of those particles was evaluated by Fourier transform infrared spectroscopy and ζ potential measurements, indicating successful functionalization and dispersal stabilization due to a mixture of steric and electrostatic repulsion. Flow cytometry revealed no toxicity of pure nanoparticles as well as hypericin without exposure to light on Jurkat T-cells, whereas the combination of hypericin, alone or loaded on particles, with light-induced cell death in a concentration and exposure time-dependent manner due to the generation of reactive oxygen species. In conclusion, the combination of SPIONs’ targeting abilities with hypericin’s phototoxic properties represents a promising approach for merging magnetic drug targeting with photodynamic therapy for the treatment of cancer.
Keywords: Hypericin; Magnetic drug targeting; Photodynamic therapy; SPION

Identification of the dominant recombination process for perovskite solar cells based on machine learning - Le Corre, Vincent Marc; Sherkar, Tejas S; Koopmans, Marten; Koster, L Jan Anton (Cell Reports Physical Science, 2021)
Over the past decade, perovskite solar cells have become one of the major research interests of the photovoltaic community, and they are now on the brink of catching up with the classical inorganic solar cells, with efficiency now reaching up to 25%. However, significant improvements are still achievable by reducing recombination losses. The aim of this work is to develop a fast and easy-to-use tool to pinpoint the main losses in perovskite solar cells. We use large-scale drift-diffusion simulations to get a better understanding of the light intensity dependence of the open-circuit voltage and how it correlates to the dominant recombination process. We introduce an automated identification tool using machine learning methods to pinpoint the dominant loss using the light intensity-dependent performances as an input. The machine learning was trained using >2 million simulations and gives an accuracy of the prediction up to 82%.

Impact of 2D Ligands on Lattice Strain and Energy Losses in Narrow-Bandgap Lead–Tin Perovskite Solar Cells - Zhang, Kaicheng; Vincze, Andrej; Metwalli, Ezzeldin; Zhang, Jiyun; Liu, Chao; Meng, Wei; Zhang, Boxue; Tian, Jingjing; Heumüller, Thomas; Xie, Zhiqiang; Luo, Junsheng; Osvet, Andres; et al. (Advanced Functional Materials, 2023)
Mixed lead and tin (Pb/Sn) hybrid perovskites exhibit a great potential in fabricating all-perovskite tandem devices due to their easily tunable bandgaps. However, the energy deficit and instability in Pb/Sn perovskite solar cells (PSCs) constrain their practical applications, which renders defect passivation engineering indispensable to develop highly efficient and long-term stable PSCs. Herein, the mechanisms of strain tailoring and defect passivation in Pb/Sn PSCs by 2D ligands are investigated. The 2D ligands include electroneutral cations with long alkyl chain (LAC), iodates with relatively short alkyl chain (SAC) and their mixtures. This study reveals that LAC ligands facilitate the relaxation of tensile strain in perovskite films while SAC ligands cause strain buildup. By mixing LAC/SAC ligands, tensile strain in perovskite films can be balanced which improves solar cell performance. PSCs with admixed β-guanidinopropionic acid (GUA)/phenethylammonium iodide (PEAI) exhibit enhanced open circuit voltage and fill factor, which is attributed to reduced nonradiative recombination losses in the bulk and at the interfaces. Furthermore, the operational stability of PSCs is slightly improved by the mixed 2D ligands. This work reveals the mechanisms of 2D ligands in strain tailoring and defect passivation toward efficient and stable narrow-bandgap PSCs.
CRIS-Team Scopus Importer:2023-07-07
Keywords: 2D ligand passivation; energy losses; lead/tin perovskite solar cells; stability; strain tailoring

Impact of a large-scale market integration on the orientation of photovoltaic modules - Bogenrieder, Josef; Hosch, Patrick; Sölch, Christian; Brabec, Christoph (2016 13th International Conference on the European Energy Market (EEM), 2016)
To increase the amount of renewable energies, the Renewable Energies Act (REA) in Germany guarantees a fixed feed-in tariff for 20 years for every kilowatt-hour that is produced. Thus, photovoltaic modules were faced in the direction of the highest energy production. In this paper we investigate, if in a future energy system with a high share of renewable energy power and especially PV power, there is an incentive to face modules divergent because of an overproduction during noon. Hence, we modelled the PV generation for the states in Germany in detail as well as the spot market for the years 2014 and 2035 according to the Grid Development Plan of the German Transmission System Operators (TSO
Keywords: Engineering controlled terms: Electric power transmission; Photovoltaic cells; Power markets Development plans; Energy productions; Future energies; Market integration; Photovoltaic modules; Renewable energies; Renewable energy power; Transmission system operators Engineering controlled terms: Electric power transmission; Photovoltaic cells; Power markets Development plans; Energy productions; Future energies; Market integration; Photovoltaic modules; Renewable energies; Renewable energy power; Transmission system operators Engineering main heading: Commerce

Impact of Aluminum Metallization Reconstruction on the Current Distribution in Power Semiconductors - Sippel, Marcel; Hassel, Simon; Schmidt, Ralf; Sprenger, Mario; Hecht, Christoph; Franke, Jörg (2022 IEEE 9th Electronics System-Integration Technology Conference, ESTC 2022 - Proceedings, 2022)
For optimized performance of the semiconductor switch in a power electronic module a uniform current distribution in the active volume of the chip is desirable. Since the bottom side of the semiconductor die is fully connected to a substrate by a soldered or even a sintered layer, the vertical current distribution is mainly determined by the top side interconnection technology and the ability of the top side aluminum metallization to spread the current in lateral direction. The focus of this paper is on the influence of the metallization and the top side connection, realized by heavy wire bonds. Sheet resistance and roughness measurements were taken on power modules, aged by active power cycling, in order to evaluate degradation during regular operation. Voltage mapping measurements across the metallization layer during operation were correlated to finite element simulation results, revealing inhomogeneities in the current density distribution in the metallization layer as well as the semiconductor die.
Created from Fastlane, Scopus look-up
Keywords: current density; degradation; metallization; power electronics; reliability

Impact of compensation on optical absorption bands in the below-bandgap region in n-type (N) 6H-SiC - Weingärtner, Roland; Bickermann, Matthias; Herro, Ziad Georges; Künecke, Ulrike; Sakwe, Aloysius; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2003)
We present an optical method for the determination of the charge carrier concentration as well as the compensation level based on absorption measurements at room temperature in n-type 6H-SiC. Below band-gap absorption bands (BBGA) are best fitted by a Fano like shape. Calibration plots are provided for evaluation of the charge carrier concentration from the peak area of the BBGA. The compensation level is derived from the comparison of the peak area of the BBGA and the absolute peak valu
Keywords: Absorption; Compensation; Fano Resonance; Nitrogen Donor

Impact of Electrodes on Recombination in Bulk Heterojunction Organic Solar Cells - Rahimi Chatri, Azadeh; Torabi, Solmaz; Le Corre, Vincent Marc; Koster, L Jan Anton (ACS Applied Materials and Interfaces, 2018)
In recent years, the efficiency of organic solar cells (OSCs) has increased to more than 13%, although different barriers are on the way for reaching higher efficiencies. One crucial barrier is the recombination of charge carriers, which can either occur as the bulk recombination of photogenerated charges or the recombination of photogenerated charges and electrodic induced charges (EICs). This work studies the impact of EICs on the recombination lifetime in OSCs. To this end, the net recombination lifetime of photogenerated charge carriers in the presence of EICs is measured by means of conventional and newly developed transient photovoltage techniques. Moreover, a new approach has been introduced to exclusively measure the bulk recombination lifetime, i.e., in the absence of EICs; this approach was conducted by depositing transparent insulating layers on both sides of the OSC active layer. An examination of these approaches on OSCs with different active layer materials, thicknesses, and varying light intensities determined that the EICs can only reduce the recombination lifetime of the photogenerated charges in OSCs with very weak recombination strength. This work supports that for OSCs with highly reduced recombination strength, eliminating the recombination of photogenerated charges and EICs is critical for achieving better performance. Therefore, the use of a proper blocking layer suppresses EIC recombination in systems with very weak recombination.
Keywords: organic solar cells; recombination lifetime; induced charges; blocking layers; bulk heterojunction

Impact of Mechanical Stress and Nitrogen Doping on the Defect Distribution in the Initial Stage of the 4H-SiC PVT Growth Process - Steiner, Johannes; Wellmann, Peter (Materials, 2022)
Nitrogen incorporation changes the lattice spacing of SiC and can therefore lead to stress during physical vapor transport (PVT). The impact of the nitrogen-doping concentration during the initial phase of PVT growth of 4H-SiC was investigated using molten potassium hydroxide (KOH) etching, and the doping concentration and stress was detected by Raman spectroscopy. The change in the coefficient of thermal expansion (CTE) caused by the variation of nitrogen doping was implemented into a numerical model to quantitatively determine the stress induced during and after the crystal growth. Furthermore, the influence of mechanical stress related to the seed-mounting method was studied. To achieve this, four 100 mm diameter 4H-SiC crystals were grown with different nitrogen-doping distributions and seed-mounting strategies. It was found that the altered CTE plays a major role in the types and density of defect present in the grown crystal. While the mounting method led to increased stress in the initial seeding phase, the overall stress induced by inhomogeneous nitrogen doping is orders of magnitude higher.
CRIS-Team WoS Importer:2022-03-25

Impact of n-type versus p-type doping on mechanical properties and dislocation evolution during SiC crystal growth - Wellmann, Peter; Hens, Philip; Sakwe, Aloysius; Queren, Desiree; Müller, Ralf; Durst, Karsten; Göken, Mathias (Materials Science Forum, 2007)
The origin of dislocation evolution during SiC crystal growth is usually related to lattice relaxation mechanisms caused by thermal stress. In this paper we discuss dislocation generation and dislocation propagation related to doping and suppression of basal plane dislocations, the latter being of particular interest for bipolar electronic devices. We have prepared alternating p-/n-/p-doped SiC crystals using the donor nitrogen and the acceptors aluminum or boron. In addition we determined the mechanical properties of n-type and p-type SiC; in particular we measured the critical shear stress by nano-indentation on c-plane and a-plane 6H-SiC surfaces. A considerably lower basal plane dislocation density is found in aluminum as well as in boron doped p-type SiC compared to nitrogen doped n-type SiC. It is concluded that the explanation of the reduced basal plane dislocation density in p-type SiC needs the consideration of electronic as well as mechanical effect
Keywords: Basal Plane Dislocation (BPD); Doping; PVT Growth; SiC

Impact of PID on industrial rooftop PV-installations - Buerhop, Claudia; Fecher, Frank; Pickel, Tobias; Patel, Tirth; Zetzmann, Cornelia; Camus, Christian; Hauch, Jens; Brabec, Christoph (Proceedings Volume 10370,Reliability of Photovoltaic Cells, Modules, Components, and Systems X, 2017)
Potential induced degradation (PID) causes severe damage and financial losses even in modern PV-installations. In Germany, approximately 19% of PV-installations suffer from PID and resulting power loss. This paper focuses on the impact of PID in real installations and how different evaluated time intervals influence the performance ratio (PR) and the determined degradation rate. The analysis focuses exemplarily on a 300 kWp PV-system in the Atlantic coastal climate. IR-imaging is used for identifying PID without operation interruption. Historic electric performance data are available from a monitoring system for several years on system level, string level as well as punctually measured module string I-V-curves. The data sets are combined for understanding the PID behavior of this PV plant. The number of PID affected cells within a string varies strongly between 1 to 22% with the string position on the building complex. With increasing number of PID-affected cells the performance ratio decreases down to 60% for daily and monthly periods. Local differences in PID evolution rates are identified. An average PR-reduction of -3.65% per year is found for the PV-plant. On the string level the degradation rate varied up to 8.8% per year depending on the string position and the time period. The analysis reveals that PID generation and evolution in roof-top installations on industrial buildings with locally varying operation conditions can be fairly complex. The results yield that local operating conditions, e.g. ambient weather conditions as well as surrounding conditions on an industrial building, seem to have a dominating impact on the PID evolution rate.
Keywords: potential induced degradation (PID); IR-imaging; performance ratio; performance loss

Impact of SiC source material on temperature field and vapor transport during SiCPVT crystal growth process - Wellmann, Peter; Hofmann, Heinz-Dieter; Kadinski, Lev; Selder, Markus; Straubinger, Thomas; Winnacker, Albrecht (Materials Science Forum, 2001)
We have investigated the impact of morphological changes of the source material during physical vapor transport growth of silicon carbide on the crystal growth process, i.e. global temperature field and vapor transport between source material and crystal? has been studied. Digital x-ray imaging was performed for monitoring of the ongoing processes inside the SiC source material. Numerical modeling was carried out to study the effect on the crystal growth process. Three different SiC sources with varying grain size were investigated. While the SiC source material undergoes fundamental transitions during growth (i.e, evolution from powder to compressed SiC block! it is found that the global growth process is more stable than one would expect. A kev role is played bp a condensed disk like structure on top of the source material which is present for all SiC source
Keywords: Numerical Modeling; Physical Vapor Transport; Silicon Carbide (SiC); Source Material; X-Ray Imaging

Impact of SiC source material on temperature field and vapor transport during SiC PVT crystal growth process - Wellmann, Peter; Hofmann, Heinz-Dieter; Kadinski, Lev; Selder, Markus; Straubinger, Thomas; Winnacker, Albrecht (Materials Science Forum, 2001)
We have studied the impact of morphological changes of the source material during physical vapor transport growth of silicon carbide (SiC). Digital X-ray imaging was carried out to visualize the ongoing processes inside the SiC source material and numerical modeling was performed in order to study the impact on the crystal growth process. According to numerical modeling there is a large impact of the SiC powder compression and morphology on the global heat transfer and mass transfer inside the growth cell. Two diﬀerent SiC sources containing microscopic SiC powder and macroscopic SiC pieces, respectively, were investigated. Although the SiC source material undergoes fundamental transitions during growth (i.e. evolution from powder to compressed SiC block) it was found that self-stabilizing of the growth process occurred by formation of a disk-like structure on the top of the source material, independent of the initial source morphology. The experimental results were conﬁrmed by the numerical simulation of the global growth process
UnivIS-Import:2019-03-21:Pub.2001.tech.ITC.stmmec.impact
Keywords: Heat transfer; Mass transfer; Growth from vapor; Single crystal growth; Semiconducting silicon compounds

Impact of source material on silicon carbide vapor transport growth process - Wellmann, Peter; Hofmann, Heinz-Dieter; Kadinski, Lev; Selder, Markus; Straubinger, Thomas; Winnacker, Albrecht (Journal of Crystal Growth, 2001)
We have studied the impact of morphological changes of the source material during physical vapor transport growth of silicon carbide (SiC). Digital X-ray imaging (P.J. Wellmann et al., Mat. Res. Sec. Symp. Proc. 572 (1999) 259) was carried out to visualize the ongoing processes inside the SIC source material and numerical modeling was performed in order to study the impact on the crystal growth process. According to numerical modeling there is a large impact of the SiC powder compression and morphology on the global heat transfer and mass transfer inside the growth cell. Two different SiC sources containing microscopic SiC powder and macroscopic SIC pieces, respectively, were investigated. Although the SIC source material undergoes fundamental transitions during growth (i.e. evolution from powder to compressed SiC block) it was found that self-stabilizing of the growth process occurred by formation of a disk-like structure on the top of the source material, independent of the initial source morphology. The experimental results were confirmed by the numerical simulation of the global growth process. (C) 2001 Elsevier Science B.V. All rights reserved.
Keywords: Heat transfer; Mass transfer; Growth from vapor; Single crystal growth; Semiconducting silicon compounds

Impact of Varying Parameters on the Temperature Gradients in 100 mm Silicon Carbide Bulk Growth in a Computer Simulation Validated by Experimental Results - Steiner, Johannes; Arzig, Matthias; Denisov, Alexey; Wellmann, Peter (Crystal Research and Technology, 2020)
The investigation of the interplay of experimental crystal growth runs and computer simulations of the physical vapor transport (PVT) growth process of silicon carbide (SiC) strongly supports the development of the growth technology toward larger crystalline diameters. To apply computer-aided designs of the growth process, a material database is developed that enables quantitative calculations of the temperature distribution inside the growth setup. The model utilizing COMSOL Multiphysics is validated by experimental means using five 100 mm SiC crystal growth runs, two measurement runs in a 100 mm PVT setup, and one SiC crystal growth run in a 75 mm PVT setup, varying in power, pressure, coil position, and reactor geometry. Material data are varied and the impact on the thermal gradients is investigated to trace out critical and noncritical parameters for the accuracy of the simulation. The influence of ambient pressure on the isolation's performance is studied experimentally and this correlation is implemented into the model. Beyond the state of the art, this work presents a modeling approach and handling of material properties for a true scale up of the current 100 mm and 150 mm SiC sublimation growth technologies to 200 mm.
CRIS-Team Scopus Importer:2019-08-27
Keywords: heat flux; induction heating; numerical simulation; physical vapor transport; silicon carbide

Impacts of carrier capture processes in the thermal quenching of photoluminescence in Al–N co-doped SiC - Tarekegne, Abebe T.; Norrman, K.; Jokubavicius, V.; Syväjärvi, M.; Schuh, Philipp; Wellmann, Peter; Ou, H. (Applied Physics B-Lasers and Optics, 2019)
High concentrations of aluminum (Al) and nitrogen (N) dopants of 6H SiC have been achieved by a fast sublimation growth process. The Al–N co-doped 6H-SiC layer exhibits a strong light-blue photoluminescence emission at low temperatures due to emissions from DI centers and donor acceptor pairs (DAP). The photoluminescence quenching mechanisms of those emissions are different. The decrease of free carrier capture cross-section as temperature increases according to the cascade capture process causes quenching of the photoluminescence emission form DI centers. Emission from Al–N DAP centers exhibits an exponential quenching with activation energy of (95 ± 10) meV. This is attributed to a competing hole capture by non-radiative defect in a multiphonon emission process.
CRIS-Team Scopus Importer:2019-08-30

Improved Air Processability of Organic Photovoltaics Using a Stabilizing Antioxidant to Prevent Thermal Oxidation - Steinberger, Marc; Distler, Andreas; Brabec, Christoph J.; Egelhaaf, Hans-Joachim (Journal of Physical Chemistry C, 2021)
During the production of organic solar cells, the exposure of constituting materials and resulting devices to light, heat, oxygen, and water is a potential source of degradation. We show that thermo-oxidation of the active materials occurs upon annealing the active layer or upon stirring the active materials solutions in air at elevated temperatures. By comparing various blends of donor polymers with fullerene or nonfullerene acceptors, fullerene is identified to be the most susceptible component to thermal oxidation in both film and solution, while the polymer remains unaffected. In both cases, the effect on the photovoltaic device performance consists predominantly in a decreased short-circuit current (J(SC)), suggesting that the underlying degradation mechanism is the same in the solid state and in solution. In addition, we find that thermo-oxidation of the active layer during annealing of the device can be decelerated by blending nickel(II) dibutyldithiocarbamate (Ni(dtc)(2)) as an antioxidant additive into the active layer. While small concentrations of additive stabilize JSC and therefore the power conversion efficiency, higher contents negatively affect device performance. On the other hand, thermo-oxidation of the active materials in solution during stirring in air at elevated temperatures can be avoided for several hours by adding as little as 0.5% Ni(dtc)(2). The observation that the antioxidant is consumed during stabilization of the active materials suggests a sacrificial protection mechanism.
CRIS-Team WoS Importer:2022-01-14

Improved charge carrier dynamics in polymer/perovskite nanocrystal based hybrid ternary solar cells - Soltani, Rezvan; Puscher, Bianka; Katbab, Ali Asghar; Levchuk, Ievgen; Kazerouni, Negar; Gasparini, Nicola; Camaioni, Nadia; Osvet, Andres; Batentschuk, Miroslaw; Fink, Rainer; Guldi, Dirk Michael; Ameri, Tayebeh (Physical Chemistry Chemical Physics, 2018)
Here, brand new ternary hybrid solar cells comprising perovskite nanocrystals (NCs) with a complementary absorption profile of the organic host matrix are reported. In particular, NH2CHNH2PbI3 (FAPbI3) perovskite NCs are implemented in bulk heterojunction organic solar cells based on the pDPP5T-2 electron donating polymer and a [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) acceptor at various loading amounts and the fabricated hybrid photovoltaics are thoroughly studied by employing different optoelectrical characterization methods. Current-voltage measurements and photoinduced charge carrier extraction by linear increasing voltage (photo-CELIV) reveal improved charge generation and charge transport properties upon incorporation of perovskite NCs into the photo-active layer of the hybrid solar cell. The power conversion efficiency (PCE) of the hybrid solar cell comprising 5% perovskite NCs is 10% enhanced compared to the organic reference, mainly due to the enlarged light harvesting and increased short circuit current density (Jsc). However, results suggest that introducing a higher amount of perovskite content induces bimolecular and trap-assisted recombination in the ternary devices. We perform a comprehensive transient absorption study of the charge transfer/transport mechanisms by employing femto-second pump-probe transient absorption spectroscopy (fs-TAS). fs-TAS measurements demonstrate a slower charge carrier recombination rate due to the introduction of perovskite NCs into the photoactive layer. Results reveal that DPP injects electrons from the singlet excited state into the perovskite NCs, which causes the desired cascading charge carrier transfer. In ternary blends, a small amount of FAPbI3 NCs provides an additional pathway in favor of the charge-separated state via the NCs, which, despite accelerating the depopulation of DPP's singlet excited state slightly slows down the charge-separation process between DPP and PC61BM. Interestingly, the loss processes are slowed down; an effect that is more important and, hence, explains the improved solar cell efficiency. © 2018 the Owner Societie

Improved Efficiency of Polymer Solar Cells by Modifying the Side Chain of Wide-Band Gap Conjugated Polymers Containing Pyrrolo[3,4- f]benzotriazole-5,7(6 H)-dione Moiety - Zhu, Peng; Fan, Baobing; Du, Xiaoyan; Tang, Xiaofeng; Li, Ning; Liu, Feng; Ying, Lei; Li, Zhenye; Zhong, Wenkai; Brabec, Christoph; Huang, Fei; Cao, Yong (ACS Applied Materials and Interfaces, 2018)
wo novel wide-band gap donor-acceptor-type conjugated copolymers, PTzBI-S and PTzBI-Ph, are designed and synthesized, based on alkylthio-thienyl- or alkylphenyl-substituted benzodithiophene (BDT) derivatives as the electron-donating unit and pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione as the electron-withdrawing unit. The as-generated copolymers show the comparable optical and electrochemical properties. The alkylthio-thienyl-substituted BDT unit facilities a benign decrease of the highest occupied molecular orbital (HOMO) levels. This consequently enhances open-circuit voltages (VOC) over 0.9 V in relevant solar cells with the fullerene acceptor ([6, 6]-phenyl-C71-butyric acid methyl ester, PC71BM) or the nonfullerene acceptor (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene, ITIC). The combination studies of Fourier transform photocurrent spectroscopy and electroluminescence further rationalize the VOC difference between solar cells with fullerene and nonfullerene acceptors. An impressively high power conversion efficiency of 10.19% is obtained for the device based on PTzBI-Ph:ITIC, outperforming the 8.84% achieved by the PC71BM-based device. Our results demonstrate that the modification of substituents of BDT units can effectively decrease the HOMO level and consequently improve VOC, ultimately allowing the attainment of high-efficiency polymer solar cel
Keywords: side-chain modification; wide-band gap copolymers; polymer solar cells; pyrrolo[3; 4- f]benzotriazole-5; 7(6 H)-dione

Improved efficiency of TiO2 nanotubes in dye sensitized solar cells by decoration with TiO2 nanoparticles - Roy, Poulomi; Kim, Dam-Hee; Paramasivam, Indhumati; Schmuki, Patrik (Electrochemistry Communications, 2009)
In the present work we investigate the effect of TiCl_4 treatments on the photoconversion efficiency of TiO_2 arrays used in dye sensitized solar cell. The results clearly show that by an appropriate treatment the decoration of the TiO_2 nanotube arrays with TiO_2 nanocrystallites of a typical size of 3 nm can be achieved. These particles can be converted to mixture of anatase and rutile phase by annealing in air. This decoration of the TiO_2 nanotubes leads to a significantly higher specific dye loading and, for certain annealing treatments, to a doubling of the solar cell efficiency (in our case from 1.9% to 3.8% of AM 1.5 conditions) can be achieved.
EAM Import::2019-03-13

Improved High-Efficiency Perovskite Planar Heterojunction Solar Cells via Incorporation of a Polyelectrolyte Interlayer - Zhang, Hong; Azimi, Seyed Hamed; Hou, Yi; Ameri, Tayebeh; Przybilla, Thomas; Spiecker, Erdmann; Kraft, Mario; Scherf, Ullrich; Brabec, Christoph (Chemistry of Materials, 2014)
No abstract available for this article

Improved properties of phosphor-filled luminescent down-shifting layers: Reduced scattering, optical model, and optimization for PV application - Solodovnyk, Anastasiia; Lipovsek, Benjamin; Forberich, Karen; Stern, Edda; Krc, Janez; Batentschuk, Miroslaw; Topic, Marko; Brabec, Christoph (SPIE Micro+Nano Materials, Devices, and Applications Symposium, 2015)
We studied the optical properties of polymer layers filled with phosphor particles in two aspects. First, we used two different polymer binders with refractive indices n = 1.46 and n = 1.61 (λ = 600 nm) to decrease Δn with the phosphor particles (n = 1.81). Second, we prepared two particle size distributions D50 = 12 μm and D50 = 19 μm. The particles were dispersed in both polymer binders in several volume concentrations and coated onto glass with thicknesses of 150-600 μm. We present further a newly developed optical model for simulation and optimization of such luminescent down-shifting (LDS) layers. The model is developed within the ray tracing framework of the existing optical simulator CROWM (Combined Ray Optics/Wave Optics Model), which enables simulation of standalone LDS layers as well as complete solar cells (including thick and thin layers) enhanced by the LDS layers for an improved solar spectrum harvesting. Experimental results and numerical simulations show that the layers of the higher refractive index binder with larger particles result in the highest optical transmittance in the visible light spectrum. Finally we proved that scattering of the phosphor particles in the LDS layers may increase the overall light harvesting in the solar cell. We used numerical simulations to determine optimal layer composition for application in realistic thin-film photovoltaic devices. Surprisingly LDS layers with lower measured optical transmittance are more efficient when applied onto the solar cells due to graded refractive index and efficient light scattering. Therefore, our phosphor-filled LDS layers could possibly complement other light-coupling techniques in photovoltaics.
Keywords: absorptance; effective scattering approach; luminescent down-shifting (LDS); Mie scattering; organic solar cell; phosphor particles; ray-tracing; refractive index; transmittance; transparent binder

Improved Thermal Impedance Measurement for Power Modules based on Thermal Imaging of the Baseplate - Sippel, Marcel; Schmidt, Ralf; Rau, Fabian; Bretscher, Daniel; Seidel, Reinhardt; Franke, Jörg (Proceedings of the 12th International Conference on Integrated Power Electronics Systems (CIPS 2022), 2022)

Improving spray coated organic photodetectors performance by using 1,8-diiodooctane as processing additive - Montenegro Benavides, Cindy; Rechberger, Stefanie; Spiecker, Erdmann; Berlinghof, Marvin; Unruh, Tobias; Biele, Markus; Schmidt, Oliver; Brabec, Christoph; Tedde, Sandro F. (Organic Electronics, 2018)
In this work, we present and support the positive influence of 1,8-diiodooctane (DIO) as processing additive for the fabrication of solution processed near infrared (NIR) organic photodiodes (OPDs) based on the spray-coated blend of [6,6]phenyl-C70-butyric acid methyl ester (PC70BM) and poly[(2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-diox-opyrrolo[3,4-c]pyrrole-1,4-diyl)-alt-([2,2’:5′,2″-terthiophene]-5,5″-diyl)] (PDPP3T). Transmission electron microscopy (TEM) analysis show that the use of DIO improves donor–acceptor interfaces in the bulk heterojunction (BHJ) layer. Besides the enhancement of electron/hole transport pathways that leads to higher efficiencies, it reduces significantly the roughness of spray coated layers. The External Quantum Efficiency (EQE) is increased up to 35% at 900 nm and the dark current is decreased one order of magnitude in comparison to the reference down to 20 nA/cm2 at -5 V. The OPD's detectivity is increased from 1.66×1011 Jones to 3.34×1012 Jones and the linearity response is improved. A comprehensive morphological and electro-optical characterization of the generated layers and devices is the main focus of this work.
Keywords: DIO additive; organic photodetectors; spray coating; BHJ morphology

Impurities and Their Influence on the Co-evaporation of Methylammonium Perovskite Thin-film Solar Cells - Borchert, Juliane; Levchuk, Ievgen; Snoek, Lavina C.; Rothmann, Mathias Uller; Snaith, Henry J.; Brabec, Christoph; Herz, Laura M.; Johnston, Michael B. (International Conference on Hybrid and Organic Photovoltaics, 2019)
In recent years power conversion efficiencies for lab-scale metal halide perovskite solar cells have risen rapidly to over 23.7% [1]. These perovskite semiconductors are advantageous due to their low Shockley-Read-Hall recombination rates, high absorption coefficients across much of the solar spectrum and high charge-carrier diffusion lengths and mobilities [2]. The planar heterojunction solar cell is a simple and popular design with the first efficient perovskite solar cell of this architecture fabricated by co-evaporation of lead iodide and methylammonium iodide (MAI) [3]. Co-evaporation of perovskite thin-films is carried out in a vacuum chamber in which two or more precursors are heated simultaneously until they evaporate. The vapours rise up and condense on the substrate which is mounted above on a rotating sample holder. Co-evaporation is a scalable process which is already used in a number of other industries and films grown via co-evaporation are uniform, have no pin-holes and are smooth over large areas [4]. This process is also solvent free which makes it fully additive and avoids the washing off of underlying layers. This is especially useful when complex layer stacks are being fabricated, for example in tandem solar cells. An important factor that will influence the commercial success of metal halide perovskite solar cells is the scalability of the deposition processes. To be able to scale a process, the reproducibility and yield of that process are both critical. In the past, several groups have encountered challenges with the evaporation of methylammonium iodide, including a variability of the chamber pressure and problems with the rate control of MAI deposition. The established method for the control of thermal evaporation processes, such as co-evaporation, is the use of quartz micro balances (QMBs). Unfortunately, it has frequently been reported, that these do not yield reliable results when used to monitor MAI evaporation. To resolve some of these challenges, we studied the role of impurities during the co-evaporation and their influence on the control of the evaporation process. To do this, we first characterised the precursor itself using nuclear magnetic resonance (NMR) and mass spectroscopy. We then evaporated perovskite films and monitored the evaporation process using quartz micro balances which are the established approach for rate control in thin-film deposition. Additionally we employed a residual gas analysis system to perform mass spectroscopy of the gas in the vacuum chamber during the evaporation. After the evaporation we characterised the deposited thin-films using a variety of methods, including scanning electron microscopy and X-ray diffraction. Finally we fabricated solar cells using MAI of different purity and measured their power conversion efficiency. Using this approach we are able to shed light on the influence of impurities in MAI on the co-evaporation of methylammonium lead iodide and the final solar cell performance. We are furthermore able to make suggestions on how to improve the control of the MAI evaporation and therefore the control over and reproducibility of the co-evaporation of methylammonium lead iodide thin-films.

Impurity Tracking Enables Enhanced Control and Reproducibility of Hybrid Perovskite Vapor Deposition. - Borchert, Juliane; Levchuk, Ievgen; Snoek, Lavina C.; Rothmann, Mathias Uller; Haver, Renee; Snaith, Henry J.; Brabec, Christoph; Herz, Laura M.; Johnston, Michael B. (ACS Applied Materials and Interfaces, 2019)
Metal halide perovskite semiconductors have the potential to enable low-cost, flexible, and efficient solar cells for a wide range of applications. Physical vapor deposition by co-evaporation of precursors is a method that results in very smooth and pinhole-free perovskite thin films and allows excellent control over film thickness and composition. However, for a deposition method to become industrially scalable, reproducible process control and high device yields are essential. Unfortunately, to date, the control and reproducibility of evaporating organic precursors such as methylammonium iodide (MAI) have proved extremely challenging. We show that the established method of controlling the evaporation rate of MAI with quartz microbalances (QMBs) is critically sensitive to the concentration of the impurities MAH2PO3 and MAH2PO2 that are usually present in MAI after synthesis. Therefore, controlling the deposition rate of MAI with QMBs is unreliable since the concentration of such impurities typically varies from one batch of MAI to another and even during the course of a deposition. However once reliable control of MAI deposition is achieved, we find that the presence of precursor impurities during perovskite deposition does not degrade the solar cell performance. Our results indicate that as long as precursor deposition rates are well controlled, physical vapor deposition will allow high solar cell device yields even if the purity of precursors changes from one run to another.
Keywords: solar cells; perovskites; hybrid metal-halide perovskites; co-evaporation; impurities; thermal evaporation; methylammonium iodide; residual gas analysis

Incorporation and control of defects with quantum functionality during sublimation growth of cubic silicon carbide - Schöler, Michael; Lederer, Maximilian; Schuh, Philipp; Wellmann, Peter (2019)
Superconductor based quantum computing has the major drawback of working temperatures which require liquid helium for cooling. A promising approach to overcome this obstacle for quantum technologies is based on deep level defects in semiconductors, with the nitrogen vacancy (NV) center in diamond being the most prominent example. Unfortunately, diamond in sufficient quality is scarce, which motivated efforts to find similar defects in silicon carbide (SiC). So far, many reports focus on investigations of point defects in irradiated 3C-SiC and as grown material. However, the investigated defects are more or less a product of coincidence for both. While in irradiated material the intentional generation of specific defects is rather challenging, in as purchased material the defects are actually more an unintentional by product of growth and process conditions. This work proposes a new route: the incorporation and control of deep level defects in 3C-SiC by epitaxial sublimation growth. The observed defects in the near infrared show bright luminescence in the 175 K/200 K regime and remain excitable up to 300 K. This could enable working temperatures above the cryogenic limit. The joint origin of all detected defects is assigned to the carbon vacancy
Keywords: 3C-SiC; deep level defects; epitaxial sublimation growth

Increased open-circuit voltage of organic solar cells by reduced donor-acceptor interface area - Vandewal, Koen; Widmer, Johannes; Heumüller, Thomas; Brabec, Christoph; Mcgehee, Michael D.; Leo, Karl; Riede, Moritz; Salleo, Alberto (Advanced Materials, 2014)
The charge carrier lifetime in small molecule: C photovoltaic devices is increased by reducing the physical interface area availabe for recombination. For donor contents below 10%, the gain in open-circuit voltage (V) depends logarithmically on the interface area while the energy of the interfacial charge-transfer state E remains invariant. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: bulk heterojunction; charge-transfer state; open-circuit voltage; organic solar cells

Increased thermal stabilization of polymer photovoltaic cells with oligomeric PCBM - Ramanitra, Hasina H.; Dowland, Simon A.; Bregadiolli, Bruna A.; Salvador, Michael; Silva, Hugo Santos; Begue, Didier; Graeff, Carlos F. O.; Peisert, Heiko; Chasse, Thomas; Rajoelson, Sambatra; Osvet, Andres; Brabec, Christoph; et al. (Journal of Materials Chemistry C, 2016)
The first oligomerisation of phenyl-C-butyric acid methyl ester (PCBM) using a facile atom transfer radical addition polymerization (ATRAP) and its exploitation for organic photovoltaic devices is described. Oligo(phenyl-C-butyric acid methyl ester)-alt-[1,4-bis(bromomethyl)-2,5-bis(octyloxy)benzene] (OPCBMMB) shows opto-electronic properties equivalent to those of PCBM but has a higher glass transition temperature. When mixed with various band gap semiconducting polymers, OPCBMMB delivers performances similar to PCBM but with an enhanced stabilization of the bulk heterojunction in photovoltaic devices on plastic substrates under thermal stress, regardless of the degree of crystallinity of the polymer and without changing opto-electronic propertie
Keywords: Engineering controlled terms: Atom transfer radical polymerization; Electronic properties; Energy gap; Esters; Free radical reactions; Glass transition; Heterojunctions; Oligomers; Photoelectrochemical cells; Photovoltaic cells; Semiconducting polymers; Stabilization; Substrates Atom transfer radical addition; Bulk heterojunction; Degree of crystallinity; Optoelectronic properties; Organic photovoltaic devices; Photovoltaic devices; Polymer photovoltaic cells; Thermal stabilization Engineering main heading: Butyric acid

Increasing the Fill Factor of Inverted P3HT:PCBM Solar Cells Through Surface Modification of Al-Doped ZnO via Phosphonic Acid-Anchored C60 SAMs - Stubhan, Tobias; Salinas Batallas, Michael; Ebel, Alexander; Krebs, Frederick C.; Hirsch, Andreas; Halik, Marcus; Brabec, Christoph (Advanced Energy Materials, 2012)
The influence of aluminum-doped zinc oxide (AZO) electron extraction layers modified with self-assembled monolayers (SAMs) on inverted polymer solar cells is investigated. It is found that AZO modification with phosphonic acid anchored Fullerene–SAMs leads to a reduction of the series resistance, while increasing the parallel resistance. This results in an increased efficiency from 2.9 to 3.3%.
Keywords: Al-doped ZnO; Aluminum-doped zinc oxide; Electron extraction; Fill factor; Inverted polymer solar cells; Parallel resistance; Phosphonic; Series resistances Engineering controlled terms: Electric resistance; Self assembled monolayers; Solar cells; Zinc oxide Engineering main heading: Organic acids

Indacenodithienothiophene-Based Ternary Organic Solar Cells - Gasparini, Nicola; García-Rodríguez, Amaranda; Prosa, Mario; Bayseç, Sebnem; Cando, Alex Palma; Katsouras, Athanasios; Avgeropoulos, Apostolos; Pagona, Georgia; Gregoriou, Vasilis G.; Chochos, Christos L.; Allard, Sybille; Scherf, Ullrich; et al. (Frontiers in Energy Research, 2017)
One of the key aspects to achieve high efficiency in ternary bulk-hetorojunction solar cells is the physical and chemical compatibility between the donor materials. Here, we report the synthesis of a novel conjugated polymer (P1) containing alternating pyridyl[2,1,3]thiadiazole between two different donor fragments, dithienosilole and indacenodithienothiophene (IDTT), used as a sensitizer in a host system of indacenodithieno[3,2-b]thiophene,2,3-bis(3-(octyloxy)phenyl)quinoxaline (PIDTTQ) and [6,6]-phenyl C70 butyric acid methyl ester (PC71BM). We found that the use of the same IDTT unit in the host and guest materials does not lead to significant changes in the morphology of the ternary blend compared to the host binary. With the complementary use of optoelectronic characterizations, we found that the ternary cells suffer from a lower mobility-lifetime (μτ) product, adversely impacting the fill factor. However, the significant light harvesting in the near infrared region improvement, compensating the transport losses, results in an overall power conversion efficiency enhancement of 7% for ternary blends as compared to the PIDTTQ:PC71BM devices.
Keywords: organic solar cells; ternary devices; OPV; IDTT; organic electronics

Industrially scalable and cost-effective Mn2+ doped ZnxCd1-xS/ZnS nanocrystals with 70% photoluminescence quantum yield, as efficient down-shifting materials in photovoltaics - Levchuk, Ievgen; Wuerth, C.; Krause, F.; Osvet, Andres; Batentschuk, Miroslaw; Resch-Genger, Ute; Kolbeck, Claudia; Herre, Patrick; Steinrück, Hans-Peter; Peukert, Wolfgang; Brabec, Christoph (Energy and Environmental Science, 2016)
We present colloidally stable and highly luminescent ZnxCd1-xS:Mn/ZnS core–shell nanocrystals (NCs) synthesized via a simple non-injection one-pot, two-step synthetic route, which can be easily upscaled. A systematic variation of the reaction component, parameters and thickness of the ZnS shell yielded doped nanocrystals with a very high photoluminescence quantum yield ( extgreekFpl) of 70%, which is the highest value yet reported for these Mn-doped sulfide-semiconductor NCs. These materials can be synthesized with high reproducibility in large quantities of the same high quality, i.e., the same extgreekFpl using accordingly optimized reaction conditions. The application of these zero-reabsorption high quality NCs in the light conversion layers, deposited on top of a commercial monocrystalline silicon (mono-Si) solar cell, led to a significant enhancement of the external quantum efficiency (EQE) of this device in the ultraviolet spectral region between 300 and 400 nm up to ca. 12%. EQE enhancement is reflected by an increase in the power conversion efficiency (PCE) by nearly 0.5 percentage points and approached the theoretical limit (0.6%) expected from down-shifting for this Si solar cell. The resulting PCE may result in a BoM (bill of materials) cost reduction of app. 3% for mono-Si photovoltaic modules. Such small but distinct improvements are expected to pave the road for an industrial application of doped semiconductor NCs as cost-effective light converters for silicon photovoltaic (PV) and other optoelectronic applications.
EAM Import::2019-03-14

Industrial viability of single-component organic solar cells - He, Yakun; Li, Ning; Heumüller, Thomas; Wortmann, Jonas; Hanisch, Benedict; Aubele, Anna; Lucas, Sebastian; Feng, Guitao; Jiang, Xudong; Li, Weiwei; Bäuerle, Peter; Brabec, Christoph (Joule, 2022)
Although the power conversion efficiencies (PCEs) of bulk heterojunction (BHJ) organic solar cells (OSCs) continue increasing toward the 20% milestone, important factors for industrial application are mostly neglected, such as photostability and cost potential. Single-component OSCs (SCOSCs) employing materials with chemically bonded donor and acceptor moieties successfully overcome the immiscibility between the donor and the acceptor as well as the resultant self-aggregation under external stress. To inspire a broader interest, the industrial figure of merit (i-FoM) of BHJ OSCs and the corresponding SCOSCs is calculated and analyzed, which includes PCE, photostability, and synthetic complexity (SC) index. Despite having a slightly more complex synthesis, all SCOSCs exhibit increased i-FoM values compared with the corresponding BHJ OSCs, and with the increase in efficiency, SCOSCs possess further potential for a higher i-FoM value. With the excellent photostability of nearly all investigated single-component semiconductors, SCOSCs are coming into the focus of attention for industrial utilization.
CRIS-Team Scopus Importer:2022-07-01
Keywords: i-FoM; industrial figure of merit; PCE; photostability; power conversion efficiency; SC index; SCOSCs; single-component organic solar cells; synthetic complexity index

Influence of a shunt on the electrical behavior in thin film photovoltaic modules - A 2D finite element simulation study - Fecher, Frank; Romero, Alexander Perez; Brabec, Christoph; Buerhop-Lutz, Claudia (Solar Energy, 2014)
Despite significant efficiency improvements of thin film photovoltaic modules over the last years, this technology struggles with the same problem - shunts that lower the output power dramatically. In this work, we studied the influence of a single shunt on the module performance by electrical 2D finite element simulations. By varying parameters such as irradiance, shunt resistance, shunt position and shunt size a profound understanding of the shunt's impact on the module performance was achieved. Most remarkable is the dependence of the module's output performance on the local shunt position, which can make up to 25% of the losses. Such high losses are caused by "circular" lateral currents in the electrode layers that spread in the shunted as well as into the neighboring cells. We show that the shunt's position inside the cell determines the geometry of the lateral currents and, consequently, the shunt's influence region.The finite element model presented here was developed on the basis of CIGS thin film modules, but the results are qualitatively valid for other monolithically series connected thin film module technologies like CdTe or a-Si:H. © 2014 Elsevier Ltd.
Keywords: 2D finite element simulation; Electrical performance; Shunt defect; Thin film photovoltaic module

Influence of a ternary donor material on the morphology of a P3HT:PCBM blend for organic photovoltaic devices - Machui, Florian; Rathgeber, Silke; Li, Ning; Ameri, Tayebeh; Brabec, Christoph (Journal of Materials Chemistry, 2012)
A comparison of grazing incidence wide-angle X-ray scattering (GiWAXS) and differential scanning calorimetric measurements (DSC) was used to identify the influence of a dominantly amorphous small band gap polymer material poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene) -alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) on the crystallinity of a semi-crystalline polymer/fullerene composite. In binary blends the low band gap polymer does not influence the crystalline part of P3HT, but does influence the crystallinity of the fullerene. In ternary blends, a significant drop of the PCBM crystallinity is observed with increasing PCPDTBT content. Adding more than 20 wt% PCPDTBT to a P3HT:PCBM blend leads to a dramatic reduction of device efficiency, mainly due to short circuit current density and fill factor losses. This deterioration is attributed to the fact that addition of more than 20 wt% PCPDTBT to the host system strongly reduces crystallinity of the fullerene phase and electron transport in the ternary system. © 2012 The Royal Society of Chemistry.
Keywords: 2; 1; 3-Benzothiadiazole; Binary blends; Crystallinities; Device efficiency; Differential scanning calorimetric measurements; Electron transport; Fill factor; Grazing incidence; Low bandgap polymers; Organic photovoltaic devices; Semi-crystalline polymer; Small band gap polymer; Ternary blends; Wide angle X-ray scattering Engineering controlled terms: Crystalline materials; Energy gap; Fullerenes; Polymer blends Engineering main heading: Polymers

Influence of blend microstructure on bulk heterojunction organic photovoltaic performance - Brabec, Christoph; Heeney, Martin; Mcculloch, Iain; Nelson, Jenny (Chemical Society Reviews, 2011)
The performance of organic photovoltaic devices based upon bulk heterojunction blends of donor and acceptor materials has been shown to be highly dependent on the thin film microstructure. In this tutorial review, we discuss the factors responsible for influencing blend microstructure and how these affect device performance. In particular we discuss how various molecular design approaches can affect the thin film morphology of both the donor and acceptor components, as well as their blend microstructure. We further examine the influence of polymer molecular weight and blend composition upon device performance, and discuss how a variety of processing techniques can be used to control the blend microstructure, leading to improvements in solar cell efficiencies. © 2011 The Royal Society of Chemistry.

Influence of codoping of YAG:Dy for high temperature phosphor thermometry - Hertle, Ellen Elisabeth; Chepyga, Liudmyla; Batentschuk, Miroslaw; Zigan, Lars (Journal of Luminescence, 2017)
The effects of codoping on the temperature-dependent luminescence of YAG:Dy were investigated for application in high temperature thermometry. YAG:Dy is a well-known thermographic phosphor suitable for high temperature measurements. However, its decay time is too long for studying temperatures in fast transient technical processes. Codoping is a known method for increasing the signal intensity and for decreasing luminescence decay times. Five co-doped samples with three different sensitizers, namely Tm, Tb and Pr were synthesized by solid-state method. Changes in spectral emission behavior and temperature dependent decay time are presented up to 1600 K. The intensity ratio used for temperature measurements was similar for all samples, and decay time decreased for all codopings. Codoping by Tm decreased signal intensity considerably, thus YAG:Dy,Tm is not suitable for high temperature measurements. However, codoping YAG:Dy with Tb and especially Pr resulted in improved luminescent characteristics, and these phosphors are promising for high temperature phosphor thermometry.
Keywords: Thermographic phosphors High temperature thermometry Codoping

Influence of codoping on the luminescence properties of YAG:Dy for high temperature phosphor thermometry - Hertle, Ellen Elisabeth; Chepyga, Liudmyla; Batentschuk, Miroslaw; Zigan, Lars (Journal of Luminescence, 2017)
The effects of codoping on the temperature-dependent luminescence of YAG:Dy were investigated for application in high temperature thermometry. YAG:Dy is a well-known thermographic phosphor suitable for high temperature measurements. However, its decay time is too long for studying temperatures in fast transient technical processes. Codoping is a known method for increasing the signal intensity and for decreasing luminescence decay times. Five co-doped samples with three different sensitizers, namely Tm, Tb and Pr were synthesized by solid-state method. Changes in spectral emission behavior and temperature dependent decay time are presented up to 1600 K. The intensity ratio used for temperature measurements was similar for all samples, and decay time decreased for all codopings. Codoping by Tm decreased signal intensity considerably, thus YAG:Dy,Tm is not suitable for high temperature measurements. However, codoping YAG:Dy with Tb and especially Pr resulted in improved luminescent characteristics, and these phosphors are promising for high temperature phosphor thermomet
Keywords: Codoping; Thermographic phosphors; High temperature thermometry

Influence of dislocation content on the quantitative determination of the doping level distribution in n-GaAs using absorption mapping - Künecke, Ulrike; Wellmann, Peter (European Physical Journal-Applied Physics, 2006)
In an earlier paper [ P. J. Wellmann, A. Albrecht, U. Kunecke, B. Birkmann, G. Mueller, M. Jurisch, Eur. Phys. J. Appl. Phys. 27, 357 ( 2004)] an optical method based on whole wafer absorption measurements was presented to determine the charge carrier concentration and its lateral distribution in n-type ( Si/Te) doped GaAs. The submitted results for Si-doped GaAs gave rise to questions concerning the interpretation of absorption mappings in wafers with high dislocation densities. GaAs substrates for optoelectronic devices are strongly affected by dislocations. Therefore further studies were conducted: absorption and Hall measurements were performed on GaAs: Si wafers with high and low dislocation densities. Absorption in Si-doped GaAs is far more complex than in Te-doped GaAs. It shows a co-dependency on charge carrier concentration and dislocation content which causes complications in the quantitative optical determination of the charge carrier concentration. Qualitatively, absorption mappings depict dislocations and variations of charge carrier concentration very well.
Keywords: GaAs; Si doping; Te doping; charge carrier concentration; absorption mapping; dislocation density

Influence of growth temperature on the evolution of dislocations during PVT growth of bulk SiC single crystals - Sakwe, Aloysius; Wellmann, Peter (Materials Science Forum, 2007)
In this paper we report, based on analysis of dislocation statistics, on the influence of growth temperature on the nucleation, propagation and annihilation mechanisms of dislocations. Using KOH defect etching and optical microscopy we have conducted dislocation tracking along lengths of crystals grown under various process temperature regimes to study their evolution and propagation mechanisms statistically. We further present the influence of growth temperature on the step structure of the growth front using AFM measurements. From the analysis of dislocation statistics and step structure in relation to temperature we derive the role of surface kinetics of the SiC gas species on the growth surface in dislocation evolution during PVT growth of bulk Si
Keywords: Defect Etching; Dislocation; Surface Kinetics

Influence of magnesium doping on the phase transformation temperature of Beta-TCP ceramics examined by Rietveld refinement - Enderle, Ralph; Götz-Neunhoeffer, Friedlinde; Göbbels, Matthias; Müller, Frank; Greil, Peter (Biomaterials, 2005)
The influence of Mg doping in Ca 3(PO 4) 2 on the transformation temperature of β-tricalcium phosphate (β-TCP) to α-tricalcium phosphate (α-TCP) was examined. A maximum substitution by 14 mol% of Mg 2+ on Ca 2+ sites in the β-TCP structure was determined for powders calcinated at 1025±10°C. X-ray powder diffraction analysis (XRPD) in combination with Rietveld method (TOPAS 2.1) was employed for quantitative phase analysis and structural refinement. The synthesized and characterized Mg-doped samples were sintered in air atmosphere in a vertical tube furnace at suitable temperatures ranging from 1460 to 1680°C and subsequently quenched to room temperature, in order to stabilize α-TCP. The β to α transformation temperatures were determined by differential temperature analysis and XRPD analysis. © 2004 Elsevier Ltd. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2005.nat.dgeo.IGM.LM.influe
Keywords: α-TCP; β-TCP; Mg substitution; Rietveld refinement; Transformation temperature; Phase transformation temperature; Rietveld method; Room temperature; Structural refinement

Influence of morphological changes in a source material on the growth interface of 4H-SiC single crystals - Arzig, Matthias; Steiner, Johannes; Salamon, Michael; Uhlmann, Norman; Wellmann, Peter (Materials, 2019)
In this study, the change of mass distribution in a source material is tracked using an in situ computer tomography (CT) setup during the bulk growth of 4H- silicon carbide (SiC) via physical vapor depostion (PVT). The changing properties of the source material due to recrystallization and densification are evaluated. Laser flash measurement showed that the thermal properties of different regions of the source material change significantly before and after the growth run. The Si-depleted area at the bottom of the crucible is thermally insulating, while the residual SiC source showed increased thermal conductivity compared to the initially charged powder. Ex situ CT measurements revealed a needle-like structure with elongated pores causing anisotropic behavior for the heat conductivity. Models to assess the thermal conductivity are applied in order to calculate the changes in the temperature field in the crucible and the changes in growth kinetics are discussed.
CRIS-Team Scopus Importer:2019-08-30
Keywords: Computer Tomography; Growth kinetics; In-situ CT; Laser flash; Numerical modelling; Source material; Supersaturation; Thermal conductivity

Influence of Plasmon Excitations in Au Nanoparticles upon Fluorescence and Photostability of Photosynthetic Complexes - Krajnik, Bartosz; Czechowski, Nikodem; Piatkowski, D.; Mackowski, Sebastian; Hofmann, Eckhard; Pichler, Stefan; Heiß, Wolfgang (Optics and Photonics Journal, 2013)
Fluorescence spectroscopy is applied to study the influence of plasmon excitations in spherical Au nanoparticles on the optical properties of chlorophyll-containing light-harvesting complexes. The separation between the two nanostructures is controlled via silica layer with varied thickness. We observe strong increase of the emission intensity for a 12- nm-thick spacer and the increase is accompanied with shortening of the fluorescence lifetime, which allows us to sepa- rate contributions of absorption and emission rate enhancement. At the same time we find an increase of photobleaching. These findings are interpreted as a result of spectral overlap between plasmon resonance and chlorophyll fluorescenc
Keywords: Plasmonics; Fluorescence; Photosynthesis

Influence of pre-existing damages on the degradation behavior of crystalline silicon photovoltaic modules - Camus, Christian; Adegbenro, Ayodeji; Ermer, Jakob; Suryaprakash, Vignesh; Brabec, Christoph; Hauch, Jens (Journal of Renewable and Sustainable Energy, 2018)
In this paper, the influence of pre-existing crystalline damage, such as cracked or broken cells or soldering failures, as they are frequently observed in operating photovoltaic (PV) plants, on the degradation behavior of mono- and polycrystalline silicon PV modules is investigated. In particular, it is analyzed if and to what extent predamage introduced prior to lamination propagates upon stress exposure. Therefore, the pre-damaged modules are exposed to various accelerated aging conditions in order to analyze the impact of the pre-damage on the degradation behavior under the respective aging scenario. In order to separate the influence of the pre-damage from composition-induced influences, the choice of materials used in the modules is varied. These investigations reveal that none of the accelerated aging tests causes any change in the pre-existing damage. In fact, the degradation behavior and rate rather depended on the choice of the module components than on the nature of the predamage. Finally, these results are compared with indoor and outdoor results obtained from other studies<br

Influence of the bridging atom on the performance of a low-bandgap bulk heterojunction solar cell - Scharber, Markus C.; Koppe, Markus; Gao, Jia; Cordella, Fabrizio; Loi, Maria A.; Denk, Patrick; Morana, Mauro; Egelhaaf, Hans-Joachim; Forberich, Karen; Dennler, Gilles; Gaudiana, Russ; Waller, Dave; et al. (Advanced Materials, 2010)
X=C or Si(Chemical equation presented)Replacing a carbon atom with silicon (see figure) on the main chain of a conjugated polythiophene gives a polysilole with higher crystallinity, improved charge transport, reduced bimolecular recombination, and reduced formation of charge-transfer complexes when blended with a fullerene derivative. Optimized bulk heterojunction solar cells using this blend give certified efficiencies of 5.2% under AMI.5 illumination. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Influence of the fullerene LUMO level on the stability of bulk heterojunction solar cells - Distler, A.; Cheon, K. -S.; Waller, D.; Guldi, Dirk Michael; Hauch, J.; Egelhaaf, H. -J. (Journal of Materials Chemistry C, 2021)
Poly(3-hexylthiophene) (P3HT) is combined with a series of C-60-based derivatives with LUMO energies varying between -3.53 and -3.83 eV, in order to study the influence of the fullerene LUMO level on the performance and stability of organic solar cells as well as the degradation of the photoactive materials. UV/vis measurements show that P3HT degrades more slowly in all investigated P3HT:fullerene blends compared to neat P3HT films when being irradiated in air. Accordingly, all fullerene derivatives stabilize P3HT against photo-oxidation, albeit to different extents, with the electron affinity of the fullerene determining the degree of stabilization. A fullerene LUMO level of -3.75 eV is found to cause maximum stabilization, while the degradation rate increases for higher and lower values. Remarkably, the higher the stabilization effect imposed by the fullerene the slower the fullerene degrades itself, which indicates a non-sacrificial mode of stabilization. Transient absorption spectroscopy measurements show similar kinetics of exciton quenching and charge generation for all P3HT:fullerene combinations indicating a similar morphology in all blend films. Inverted solar cells made from the different P3HT:fullerene blends exhibit a good correlation between fullerene LUMO level and open-circuit voltage. Upon illumination in air, the photovoltaic devices follow the same degradation trend as the isolated photoactive layers by showing the same dependence on the fullerene LUMO level. Finally, we discuss different mechanisms, by which fullerene acceptors are potentially able to stabilize (UV light screening, excited-state quenching, and radical scavenging) as well as destabilize (morphological effects, superoxide or singlet oxygen sensitization, and polymer triplet-state population) donor polymers.
CRIS-Team WoS Importer:2021-07-23

Influence of the growth conditions on the formation of macro-steps on the growth interface of SiC-Crystals - Arzig, Matthias; Künecke, Ulrike; Salamon, Michael; Uhlmann, Norman; Wellmann, Peter (Journal of Crystal Growth, 2021)
Several SiC crystals were grown in the same temperature field with a variation of the gas phase and the resulting step morphologies on the surface are analyzed using Laser Scanning Microscopy (LSM). It is shown that the step morphology changes due to doping, but also due to different C/Si ratios in the gas phase. By the addition of graphite into the source powder a reduction of Si-excess was achieved and an ordered step structure with an average height of 0.014 µm and width of 5.0 µm was formed. In the n-type doped case (n = 5.9∙1018 cm−3) the morphology on the facet differs strongly. Bunched steps with heights of 0.17 µm and widths of 152 µm are found. Between the diverse large macro-steps, a very ordered structure of unit cell height steps with a step spacing of 13.3 µm is found by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM). A different change in the step morphology occurs over the whole crystal surface when elemental silicon is added into the source material. In contrast to the doping induced case, the bunched steps are more closely spaced and exhibit average heights of 0.20 µm and widths of 22 µm. The steps are noticeably retained at defects like micropipes or threading dislocations. The N2 induced step bunching is related to step kinetics on the main facet but the formation of macro-steps in the Si-rich case is assigned to the formation of stable surface steps. The variation of the inert gas pressure in the growth cell also changes the C/Si ratio in the gas phase as the diffusion from source to seed of the reactive gas species is affected differently. With a low inert gas pressure of 0.2 mbar a larger C/Si ratio in the gas phase is formed leading to steps with heights too small for analysis in the LSM, while the growth in 40 mbar promotes a smaller C/Si ratio leading to the formation of bunched steps with heights of 0.10–0.20 µm and with an average distance of 4.3 µm between them. The crystals grown in a gas phase comprising a large C/Si ratio show a better polytype stability than the crystals grown in Si-rich conditions. The instabilities can partly be attributed to the pile up of the macro-steps at defects exposing large 0001¯ terraces, where 2D-nucleation of foreign polytypes can occur.
CRIS-Team Scopus Importer:2021-10-29
Keywords: A1 Surface structure; A1. Optical microscopy; A1. Step bunching; A2. Growth from vapor; A2. Single crystal growth; B1 silicon carbide

Influence of the growth interface shape on the defect characteristics in the facet region of 4H-SiC single crystals - Arzig, Matthias; Salamon, Michael; Hsiao, Ta Ching; Uhlmann, Norman; Wellmann, Peter (Journal of Crystal Growth, 2020)
Two 75 mm 4H-SiC single crystals are grown by the physical vapor transport (PVT) technique, using different insulation materials. The insulation material of higher thermal conductivity led to an increased radial temperature gradient. The evolution of the growth front was monitored using the in-situ computed tomography (CT). A slightly bent growth interface and a bigger facet are formed during the growth applying a lower radial temperature gradient while a smaller facet and steeper crystal flanks are formed in the case of the larger radial temperature gradient. Micropipes are deflected laterally by large surface steps on the steep crystal flanks and a reduction of threading edge dislocations by 60% is revealed by KOH defect etching.
CRIS-Team Scopus Importer:2019-12-31
Keywords: A1. Crystal morphology; A1. Defects; A1. Surface structure; A2. Growth from vapor; A2. Single crystal growth; B2. Semiconducting silicon compounds

Influence of the Hole Transporting Layer on the Thermal Stability of Inverted Organic Photovoltaics Using Accelerated-Heat Lifetime Protocols - Hermerschmidt, Felix; Savva, Achilleas; Georgiou, Efthymios; Tuladhar, Sachetan M.; Durrant, James R.; Mcculloch, Iain; Bradley, Donal D. C.; Brabec, Christoph; Nelson, Jenny; Choulis, Stelios A. (ACS Applied Materials and Interfaces, 2017)
High power conversion efficiency (PCE) inverted organic photovoltaics (OPVs) usually use thermally evaporated MoO3 as a hole transporting layer (HTL). Despite the high PCE values reported, stability investigations are still limited and the exact degradation mechanisms of inverted OPVs using thermally evaporated MoO3 HTL remain unclear under different environmental stress factors. In this study, we monitor the accelerated lifetime performance under the ISOS-D-2 protocol (heat conditions 65 °C) of nonencapsulated inverted OPVs based on the thiophene-based active layer materials poly(3-hexylthiophene) (P3HT), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), and thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTTT) blended with [6,6]-phenyl C71-butyric acid methyl ester (PC[70]BM). The presented investigation of degradation mechanisms focus on optimized P3HT:PC[70]BM-based inverted OPVs. Specifically, we present a systematic study on the thermal stability of inverted P3HT:PC[70]BM OPVs using solution-processed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and evaporated MoO3 HTL. Using a series of measurements and reverse engineering methods, we report that the P3HT:PC[70]BM/MoO3 interface is the main origin of failure of the P3HT:PC[70]BM-based inverted OPVs under intense heat conditions, a trend that is also observed for the other two thiophene-based polymers used in this study. © 2017 American Chemical Society.
Keywords: Butyric acid; Conducting polymers; Degradation; Hole mobility; Molybdenum oxide; Reverse engineering; Stability; Thiophene; Degradation mechanism; Hole transporting layers; Inverted structure; lifetime; Organic photovoltaics; Thermodynamic stability